My old org had a very liberal (in the correct meaning of the word) firearms policy, including modifications.
Any mods, excluding lights, had to be supported by an armorer and approved by the program manager. That was a large part of what allowed me to spend all of 2012 working patrol with an optic on my pistol. WML were not considered modifications.
A few people would try to bypass it every so often. But that generally got caught and addressed.