Go for it.
Foremost, I wouldn't consider lightening a new set of gears or sprockets to be altering their function. I wouldn't even say that changing ratios is altering function so much as it is altering performance. In my mind, that's okay.
There is no rule (yet) that prohibits making parts after the robot has shipped. I have reviewed the entirety of the rules as well as each team update. In fact, in the rules, there isn't even anything that say such parts must be identical spares.
Of course, in past years, fabrication had to cease on ship day. I think that many teams may be operating under the impression that this is the case this season.
However, upon further inspection, I found this on FIRST's message boards:
http://jive.ilearning.com/thread.jsp...073686970#4432
In that post, FIRST says that only identical spares may be made.
But, in a later thread (
http://jive.ilearning.com/thread.jsp...073686970#4732) FIRST replied somewhat differently.
Does the newer response supercede the old one? In the case of all else that's happened on those message boards, it has. So, then, is it safe to assume that's true of this as well? It may become of matter of semantics.
Where I'm concerned, go ahead and make what changes you need to make. If FIRST, in a forthcoming update, says we should stop -- stop.
This discussion is of great interest to me. We have already planned a major retrofit for our design to make it more versatile and that retrofit requires new parts. We're hoping to build a prototype of it now, as there's no hope of finishing it before FIRST says to stop building parts, and then make a final version after our first regional -- keeping in line with rules from years past, as this years rules are something less than crystal clear.