Add Exisiting Domain user to Local Computer with Powershell

Question

I'm trying to automate the desktop file migration of user accounts for some of our legacy users. I have a powershell script that can remove them from whatever domain the may be joined too, then join our current domain. But I want to copy files from the old user account to their new domain account, but how can I add the domain user profile to the local computer without breaking my powershell script and then starting it again.

I've got Admin access to Local Machine, New Domain, and User credentials. Just need something like Add-User -Credential $USRcred -DomainName $DOMAIN or something. My users already exist in the new domain, I just need their user profile downloaded/setup on the local machine.