Hey there hbwall,
We understand you have a question about whether migrating a user account to your MacBook Pro will impact existing user accounts.
It looks like you've already reviewed Move your content to a new Mac.
Migrating a user account shouldn't impact any of the existing accounts, unless the new account has the same name as an existing account. The details below have more information:
"If it has the same name as an account already on your new Mac, you're prompted to either rename the old account or replace the one on your new Mac. If you rename, the old account will appear as a separate user on your new Mac, with a separate home folder and login. If you replace, the old account will delete and then replace the account on your new Mac, including everything in its home folder."
To best protect against any data loss, back up your Mac prior to migrating the user account.
We hope this helps.