I am helping my nephew get a start in bike racing and I just realized he is subject to gear restrictions for sanctioned road races. His bike is a cross bike, so it has a 48 big ring. The smallest gear in back he can use is a 13 with the gear restrictions. However, the only cassettes I can get on short notice have a 12.

Will the refs let me lock out the smallest cog (crank in the set screw) so physically it passes the roll-out test? Or will there be issues with the fact that the bike could be modified to to cheat?