CF hood can be lighter than stock hood. If you let people run CF hoods then in order to have a competive car you would need to have a CF hood (weight matters). The CF hood is the only one there that bumps you to a real hard class. The other mods would just put you into STS.
I have seen a different ruleset (either midwest of Canada I think) that give points based on different mods (like replacement hood +2 points, different wheels +1 point) and how many points you have determines your class I would guess they also class cars but I dont remember the whole ruleset.
If you are just a weekend person out there to have fun what do you care about what class you are in or how you place in the class you go into? Just run for fun with your friends and see who is the better driver.
I know at least one local driver that switched cars just to be competetive in Stock class AutoXing.
