For lack of more technical terms, the MIB does not care about the BCM. It's not even something you need to think about when doing the BCM. The first time I replaced my BCM I had already done MIB 2 retrofit. My third and fourth BCM, facelift BCMs, I had already done MIB 2.5. No impact at all.
If you have the dealer do the BCM replacement you don't have to worry about coding or adaptations. I did not buy my BCM from the dealer. They had never done it but they looked up the book time for BCM replacement and I believe it was 4 hours. As I mentioned before, I got access to the BCM, which is really just removing some trim pieces. So they cut their quote down to 3 hours.
Of course your dealer might be more willing to replace the BCM if you also buy it from them. And that of course means paying their price. I don't know what that might be. Used BCMs, even facelift high ones, can be found for about $125 on eBay. So it may well be worth trying to convince them to install your customer supplied part with the agreement that they are not going to long-term warranty their work. By that I mean they have to get it working before you drive off the lot, but they aren't going to give you a 6/12 month or whatever their standard warranty is.
There is a 100% fully guided function for replacing the BCM. As long as they follow that it will take care of component protection, keys, coding and all adaptations. Keep in mind that the high module has all of the features of anything lower and then some... Of course that's why you're going to a high anyway.
When they follow the guided function, their diagnostic software is going to pull your VIN and then do all of the coding and adaptations that are applicable. It's always advisable to make VCDS backups, those instructions are on the Ross tech website. But... If the dealer follows the guided function there's actually no need for those backups. You won't have to do anything in VCDS until it's time to code things that your car didn't come with, like heated seats, fog, lights, etc.