No I have not much of an idea for a blanket alterations for change in weight class. I was thinking about it for one of my universes but didn't come up with anything I was particularly happy with. The system I started with was when a fighter moved up a division (a real division, not Jr Fly to Fly for example) there is a chance that their CF, HP and Chin ratings. I rolled a 6 sided dice, on a 1-2 the rating got worse by 2 points, 3-5 got worse by one point and on a 6 it stayed the same. Of course you have to adjust the 3pt puches to match the new HP rating.
Best I have come up with...
Mark