TheoA,

Print yourself a copy of the Nacra Class Rules.

http://members.tripod.com/UNI55/inca.htm

You can't modify much without being out of the class rules.

I couldn't sail in the recent Performance Nationals that took place in my backyard, because my Nacra 6.0, brand new sails were not made by Skip Elliot nor purchased from Performance.

But, that's another story........