This all depends on how handy you are at working with small parts and very close tolerances.
This IS a critical safety device, and if it isn't fitted PERFECTLY, you have an unsafe gun that's an accident looking to happen.
People do fit their own 1911 safeties, but you need to know EXACTLY what you're doing and what needs to BE done.
If you're not totally confident in your manual skills, totally familiar with the 1911, or don't have a good magnifier and some other tools, let a pro do it for you.