I'm more of a shooter than a pure collector. To me anything that makes the gun more functional to its owner is acceptable. Even if its simply cosmetic work. Its your gun so fix it up any way you like.
However, I also feel that any restoration back to factory or near factory condition should be clearly marked in order to prevent fraud.
Changing the gun to a rarer or more collectable configuration is totally unacceptable. In my mind that would amount to intentional fraud.