I'm not sure what you mean by "with HP/MP/variables," but what you're asking about generally is called "transforming" the enemy - if you Google that, you'll find a Yanfly Tip & Trick about it, as well as many other threads here.
If you still have questions after trying to use those, let us know what part of it you're stuck on.
Let it be known that I am very forgetful, and I often forget that I was engaged in conversation with people
here (and every other community I'm on). So if I ever stop replying to PMs or comments, please don't take it personally and just send me a reminder to reply XD