It has been in the back of my mind recently to switch my Google account to a different Gmail address. In my case, my primary Gmail address is an unprofessional gaming nickname while I have a newer Gmail address that is more professional. My setup was to have my new Gmail forwarding to my old Gmail and I have it set up as a secondary send-as address. Unfortunately, some email clients will render emails from my account as “NewAcct@gmail.com sent on behalf of OldAcct@gmail.com” which kind of defeats the purpose.
I would like to make my newer address my primary Google account. Other common instances where people want to change to a new Google account include name changes like going from your maiden name to your married name, say Susan.Test@gmail.com to Susan.Example@gmail.com.
With the task in mind and getting a new Android phone, I set to work on switching my primary Google account. With all of the various Google products kept a little separate, I wanted to go through the most popular ones that I use to see how the transition will go – what will need to be recreated, what content can be transferred, what products can be delegated, and what might be a show-stopper to the transition. Some of this might be specific to me and my priorities but still provide a template to others in the same boat.
Gmail
Transferability: 
Gmail has the benefit of being built on email standards. Even if it uses labels a little different than folders, its compatibility with a simple IMAP client means that you can move conversations between accounts by connecting both accounts to a client like Outlook and letting it do the work. That takes care of messages and labels but you will need to reconfigure any special settings such as signature, filters, and Gmail behaviors.
Google Calendar
Transferability:
Google Calendar allows you to head into the settings and export your calendars as ical format and import them to your new account. You can also share your calendar from your old account to your new account, if you would prefer going that route. Speaking of sharing, you will have to share your calendar again and get people to share their calendar with your new account if you used that feature.
Android/Google Play
Transferability: 
Your Android smartphone or tablet uses your Google account but it really seems to pull everything together to make your device work for you. The main impact your Google account has on Android comes from Google Play, keeping track of the apps and media that you have bought or downloaded. You can compare from one device to another to get everything setup the same way but if you’re talking about paid apps or purchased digital media, you are going to have to buy them again.
Google Play Games
Transferability:
A relatively newer feature of Google Play is the hook into popular games that developers can take advantage of. Games can automatically save their progress to your Google Play Games account, keeping multiple devices synchronized or backing up your progress in case something happens.
The main game that I play on my phone is Plants Vs Zombies 2 and I wished to transfer my progress to my new phone on my new account. I was able to launch the game, sign out of Google Play Games on my old phone, sign in with my new account and it backed up the progress to my new account. On my new phone, I launched PvZ2 and signed in with my new account. My progress and status was transferred over completely. The only thing that wasn’t transferred was the achievements I have earned with my old account.
Google Drive
Transferability:
Google Drive is similar to Gmail and Google Calendar. There is nothing to stop you from downloading all of your old files and uploading them to your new account. It’s inconvenient but doable. The main loss you will experience with Google Drive if you’re a heavy user is that you will have to share all of your files again and get files shared with you again. You could also share your files from your old account to your new account. That takes less bandwidth and would give you the ability to view and edit your files (depending on the permissions you give the shared files) but the old account would remain ‘owner’.
Google Analytics
Transferability: 
Google Analytics is quite comprehensive on transferring the properties to multiple accounts. As multiple people might want to access a site’s statistics, Analytics makes it easy to add users and give them varying levels of permissions. For each property, head into Administration, User Management. Then Add the new email account and select the full permissions to pass the site to your new account.
Google Adsense
Transferability:
With Google AdSense, there is one gotcha with transferring the AdSense property – your new account cannot already have an AdSense account. In a previous attempt at transferring, I setup AdSense on my new account and was just going to reproduce everything over. My new account was denied, which kept me from proceeding. Six years later and I went to transfer my AdSense account to my more professional Google account and it got in the way saying it already had an AdSense account. I was able to contact AdSense support and they deleted my new account’s AdSense account (no loss since it was denied way back when).
In AdSense, you can find User Management under the Gear, Settings. Then under Access and Authorization, User Management, you can invite your new Google account by its email and make it an administrator. You’ll get an email to the new account saying that it has been invited to AdSense and follow the directions to confirm.
Webmaster Tools
Transferability:
Webmaster Tools is one of the Google products that I could probably setup from scratch and not miss anything. However, they make it easier than that by adding a new user per property.
Choose Manage Property, Add or Remove users, and then Add a new user and select the permissions needed (full or restricted). You also want to follow the ‘Manage property owners’ to give more access to your new account assuming you might get rid of your old account at some point. While you might have previously verified your site by putting a file on the root of the domain or by using Google Analytics, this transfer will be marked as verified by delegation.
Youtube
Transferability:
I had plenty of fun straightening out my YouTube account after it became tangled up with Google+, so I was not looking forward to this component again. Fortunately, the 404TechSupport channel that I care about is a separate Google+ page/YouTube channel. That allows me to add managers and make my new account to be a manager of the page, which gives me full access to the channel.
My individual user’s channel though was seemingly lost. I could download the videos and reupload them but that was about it. The channel name would be lost as would any subscribers or comments.
Google+
Transferability: 
Google+ is the root of your Google account. Nothing transfers. Start from scratch by manually copying your circles, posts, and anything else you care about. Fortunately, I don’t care much about my Google+, so while this was the most limited product I encountered, it wasn’t a showstopper for me.
Google Domains
Transferability:
Google Domains is fairly basic in its settings but they have the standard domain transfer process. It’s actually smart enough to know if the domain is held by Google Domains in another Google account and simplifies the process greatly. You can sign in with both accounts simultaneously and switch back and forth to initiate the transfer, get the authorization code, and submit the authorization code. It gives the option to copy all settings with it or start fresh. There is even a Help document to walk you through it.
Contacts
Transferability:
Google Contacts recently got a redesign. You will have to hop into the old view but from there you can export your contacts as a Google CSV format (for importing into a Google account) and then on your new account, again in the old view, import the contacts. It’s doable but not a great sign that it’s not available in the new look yet.
Google Maps
Transferability:
Google Maps is more something that I use when I need to look up directions and I rarely revisit them. You can create your own maps though and those I did not find any way to transfer though you can share them to your new account.
Google Finance
Transferability:
Google Finance is a pretty simple product that monitors the complex stock market. It does allow you to create portfolios to tracks the stocks that matter to you with your quantity of shares and purchase prices. From each portfolio, you can export it to a CSV or an OFX file. (I found the OFX file to work best while the CSV dropped certain values.) You may then import the transactions into the new account.
Google Voice
Transferability:
You can only transfer your Google Voice number. This means that none of your text messages, call history, voicemail, settings, or forwarding phones will be transferred.
You cannot transfer your Google Voice number onto an account that already has a Google Voice number but you could delete the number that you did not want.
You will find this option under Settings, Voice, Transfer (next to phone number).
Conclusions
I was able to successfully migrate from one Google account to another. Unfortunately, there is no simple ability to merge or change a Google account to a different name. It was time-consuming and a mental exercise to keep track of all the Google products but it worked and nothing has seemingly fallen through the cracks. If you find yourself in a similar situation, best of luck and keep the Google Takeout service in mind to get a copy of all of your data if it comes to that.