The Safetys will in theory change out, but may require fitting, and if they were already fitted to another gun, there is the possbility that too much metal was removed, the safety can't correctly be fitted to another gun, if one of them was out of spec a little bit.
The other thing is not all safetys are equal, aftermarket safety for the 1911 vary quite a bit in quality, and some work better then others. When fitting a new safety to a 1911, and I have done several because I am left handed and often had to change out to an ambi-safety, I have found that sometimes to get it just right, may take an hour, depending on how well it goes, or might take 3 hours to get just right.
The thing I am picky about is I hate a mushy safety, and I want a safety to go from one postion to the other with a definate and just the right amount of snick, click, snap, whatever you want to call it. And that is sometimes a challenge, and may even require a plunger spring change or reshaping slightly to get it just right, but once right, it usually continues to work flawlessly from then on.