I imported a Samsung Note 20 Ultra from Hong Kong and had the same experience with Samsung Pay not working.
I used Google Pay instead which I think is a better option than potentially causing issues.
In regards to carrying out what you speak of I'd suggest to look at sites such as sammobile.com and xdadevelopers.com and reddit.
You would also have to research if your phone's csc can in fact be changed.
A Google Search is your friend too.
Please be careful as not to cause any possible instability of your phone @RuthlessAfro24
This is from a forum search >
There are more via a search.
As a final note please do consider Google Pay.
I wish all the best.
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I'm here to help. " This is the way. "
Hello, maybe BTU firmware you downloaded has XEO csc instead of BTU as the Multi-CSC is same, OXM. There may be no solution for locked devices to change CSC. Visit Samsung Service Centre.