I have a Ruger P94. I have 2 California 10 round mags for it & I bought a 15 rounder for it. In looking at the 15 rounder, i noticed that it is identical to the 10's with the exception that the floor plate inserts go further up in the 10 rounders, making it carry less rounds. Does anyone know if floor plates are available to change them to 15 rounders? And has anyone done this?

That is not how they work. The metal bodies are physically smaller. You cannot take a 10 round magazine and make it a 15 round magazine.