I've been having this issue for a long time and never have found a solution. My problem appears when I want to modify the design of a specific zone of a part (this part will upgrade its revision), but this modification is compatible with its previous revisions, so no assembly will be upgraded. If the modified zone of the part wasn't used for mating with other components in the assembly, no change would be neccesary in the assembly file, but, as the change I'm talking about is in that area, mates would crash.
Is there any way to modify a part keeping the assembly mates working without modifying the assembly?
Thank you very much for your help.