Hi @liochan you will find some fairly entry grade information on the general subject and sources of Stock ROMs (I know no official Samsung ROMs published openly) are in
Samsung have a way to protect themselves and to make evidence to help them deny responsibility in the event of use of any custom software.
If you turn to the Download screen of a Samsung you will find the item
WARRANTY VOID:
- 0 (or variant of zero) is no Void, warranty intact.
- 1 (or variant of one) is effectively “Your warranty is void”
This will change (from 0 -1) the moment you change away from official Samsung firmware.
Change back to stock ROM the phone will behave as original, except for this “hidden” detail.