Australian Concert Bands

I have a question:

If a band wants to take a clarinet quartet to Nationals but doesn't have a bass clarinet player, can one of the clarinet players play bass clarinet, even though they play Bb clarinet in the band competition? I know the rules state that you can't play different instruments in the same competition but does that go for instruments in a similar family?

ie alto sax playing in band competition but playing a soprano sax in a quartet
trumpet player playing in band competition but playing cornet in a quartet

Any help on this (particularly anybody associated with the organising of 2009 Nationals) would be much appreciated.

Cheers, Nicole

i think it would depend on what instrument the player is registered on