We don't want to update parties via the losing source system

Business requirement- After merging two parties, both the parties source system references are retained in the master party.

Current case- We get updates from losing as well as winning source system reference.

Future case- Business doesn't want to update the party level data from losing source system. How to identify after merge, which source system is the losing source system and which one is winning. Please let us know which options are available to cater to this business requirement.