[EricH]

Back when I was involved with FLL teams, there weren't really restrictions on what could be changed when teams were at the table, as long as they had the parts there. I'd check the rules to make sure that parts changes aren't prohibited, and if they aren't, have at it.

And while you're at it, this is a great chance to teach the kids how changing one element often requires changing other elements... if encoders or timers are used to control distance, changing wheels could very well throw them off if they're set for the original wheels. That should be easily manageable, though, so it's a teaching experience instead of a learning experience.