I am planning on teaching my Espeon Hidden Power and I was wondering if the type and power of Hidden Power can change after I teach it to him through my training? I know that Hidden power is based upon my stats and EV's that Espeon will have, but I admit that I don't really know all that much otherwise about how it works and so I was wondering if it would transition to a new type and power after training and everything?
No, it is an individual value. And IVs cannot be changed. You'll have to breed more Pokemon.