Migration Assistant question re: 'new' user name

I'm looking to migrate from a 2012 Mac Mini that was in High Sierra - to a 2018 Mini. I created an external HD boot drive with Mojave, and backed the contents of the 2012 to that disk. I am now at a point where i want to migrate it to the newer machine. On the newer machine, I installed Mojave and, had to create a user name/account in order to go into Security preferences and "allow" external bootability, "authorize myself" as an admin., and so on.

Now I want to use MA to transfer the old Mini contents onto the '18 internal drive.

Some of my apps under the user ID of the old machine have authorizations that are tied to the User name on that machine. I'd like to keep those intact and not have to reauthorize things - which, when I've just 'cloned' a drive in the past, wasn't an issue. Do those get "carried over" onto the new HD with MA?

If I use MA it gives an option of replacing the target drive User with the User name of the source disk system - which sounds like what I want/need, but -- there's another option to make that source machine a separate User from the one that already exists on the target HD. So, since I already had to create that new machine "user" id ... if I choose to replace it with the one from the source disk, what happens to the permissions/authorization and "admin" data associated with the newer machine User id? Does it get transferred to the "new" user ID name? Or, do i encounter some sort of roadblock where i need to make the User the administrator "again" - after MA is done?

Thanks for any hints or suggestions! Really appreciate it.

Mike