Migrating from one 365 tenant to another

 We recently converted a portion of our company from one 365 tenant to another.  

Here's what we did

From a PC perspective, we had the users do the conversion of the machine.  They just followed a 50-step guide with pictures of what to do, had around 200 users do it themselves.  IT would remote in once in a while when something occurred that didn't match the document, but was minimal overall.

We had them add a 'other users' account to the computer.  This account was given administrative privileges and allowed them to use this account to facilitate the switching from one 365 domain to another

Once they added the local admin account, it was then logged into.  The account name was "conversion" in this example

Then they disjoined from the work/school domain 

When disjoined, MS has you do an account check to ensure you can log back into the computer.  Users just used the local admin "conversion" account they created.

Computer is rebooted and the users log back into the local account

They re-add themselves to the new 365 account.

Its important that they use this option and not the top one.

Assuming you have MFA setup, they will be challenged to setup their MFA access

Once this authentication is working, they will then be prompted to JOIN and then reboot.

We used a sperate tool to migrate email and OneDrive, but it could be manually done, but its time consuming.

BitLocker keys transferred during this process

The original 365tenant user account was still on the machine and could be accessed.

Once users confirmed their data was done, they self-deleted the admin account and their old user account.

The actual conversion from one tenant to another only took about 30 minutes.  

We had contingency in place in case users had issues and needed to revert back to the original tenant, which they could, but it wasn't needed.