[Solace]

I think that the spirit of the rule in this case is that a team should not continue work on the functionality of their robot after the 6 week deadline. If you're doing this simply to make weight - while it is still technically against the rules - it wouldn't particularly bother me. Still, the best choice would probably be to buy the sprockets (which is legal) and lay them out for machining at the competition itself.

[edit]
clarification: what you are suggesting does violate the letter of the rules, but not the spirit of the rules. While I would suggest following the rules, I don't think - seeing that such a modification wouldn't actually change the functionality of you're robot, only help it pass inspection - that anyone will care much.

Of course, that's just my opinion. Personally, our team has never been faced with this problem, but as long as such a modification doesn't give an unfair advantage I don't really care.
[/edit]