You body shop guys have probably removed and installed key locks in doors a hundred times. Whats the secret in removing the lock keeper from inside the door skin ?

I don't think there is any "secret", it just slides out. I have over the years used a long screwdriver, pliers, etc. I have found that my right angle needle nose pliers work best. I grab it and twist the pliers so the top of the clip pulls out a little, then the bottom, then the top and it comes out pretty easy.