Not done it but understand your concerns about losing power and having to reset and/mess up stuff.
One way to keep 12v always there is :
using eg battery jump leads, attach the new battery in parallel to the existing one, then perhaps with some help, lift the old one out, insert new one, keeping everything connected so the cars always got 12v on it, transfer the battery cables from old to new, remove old battery and all done. Not difficult but a fiddle perhaps.
Let us know how you get on, with pics of course.
2018 718S, UK, various extras, almost perfect!, Gyeon Ceramic coating, reversing camera, front view camera, Blackvue 900S twin 2 ch x 2 = 4 cameras.