I have the same question. BGA resoldering isn’t a concern, there’s another tricky thing - EFI and configurational smds on the board. For instance, if you want to upgrade RAM it’s tottaly doable except you MUST KNOW which smd configuration is needed for your new setup, so you have to change it in a very special way.
Is that the same for CPU? Or the work is to simply resolder the new chip?