From what papyrus has said, you'll be fine as long as you don't change
those portions of the text files that control the performance of the
car and track conditions. Changing the mirrors should have no effect
on a multiplayer game.
--
Emory University Graduate School of Arts & Sciences
The IWCCCARS Project: Q & A Representative
Nascar Setups Page: http://www.racesimcentral.net/~ebusch/