Is it possible to change the tolerance standard without Creo changing explicitly set tolerances?

We have dozens of older parts/drawings that were made before we found our footing with Creo... Now, whenever we open an older part/drawing and try to bring it up to snuff (adding shaft tolerances, using the block tolerance for what doesn't need to be explicit, etc.) someone has to make a note of all the existing tolerances because changing from ANSI to ISO changes all the explicitly set tolerances to the "standard".

I understand this might be useful to some people, some of the time - but am I really to understand that this "best of the best" software package isn't smart enough - or can't be configured - to leave what is explicitly set, well enough alone?