Maybe it depends on the recipe as to how well the rebatch will turn out.
I've done a couple of rebatches that came out fine. All I did was put the soap through a cheese grater, put it in a large pot and heated it on medium. My stove is electric which doesn't get as hot as gas ones do, or so I've been told. I kept an eye on it at all times. Once it started melting I'd add a little coconut milk to smooth it out and continued to do so: heat and a little milk until it was the consistency I wanted it. Just watch the milk, too much and it's ruined. I didn't use any water.
It spent a couple of days in the mold and once it felt hard enough I took it out and soap! It wasn't as hard or smooth as my cp soap, but I like it, I plan on doing some more.