I think the answer to the question is fairly obvious--altering a collectible gun ruins its collectibility, and it really is a lost piece of history at that point.

However, what I think would be a more valuable question to ask is why people get jumped on when they propose making changes to a gun that has ALREADY been altered?? It's no longer original, so nothing is lost--what's the big deal with making whatever alterations will give the user pleasure at that point?