I didn't make the rules. The CMP did, and for safety reasons.
However as a CMP GSM MI, I'm bound to follow their rules. It's not really hard to tell if a serial number has been modiified.
When in doubt, I error on the side of Safety.
I do take rifles to matches for those who don't have rifles and want to shoot a CMP Clinic/Match. Anyone is more then willing to shoot my rifles.
The rules weren't put in place to prevent people from shooting, they are there for safety issues.
CMP Competition Rules. 16th Edition -2012
6.3.3 As-Issured M1903 Springfield:
Caliber .30 U.S. Model 1903 Springfield rifles manufactured by Springfield Armory with serial numbers of 810,000 or lower or by Rock Island Aresenal with serial numbers of 285,506 or lower may not be used in any CMP-sanctioned competition.