I'd suggest to head over to sammobile.com and xdadevelopers.com where you will see posts from Members and tutorials.
However please be extremely careful as not to cause stability issues.
Unless Calling over Wi-Fi is a must and as the phone is working well I'd personally leave the CsC and firmware well alone.
If things go wrong then Samsung UK may not be able to help due to its grey import status.
I wish you all the best with this situation.
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. "