What you just described is called 're-batching', and yes, you can do that. You'll just need to grate your soap up with a cheese grater and cook it on low heat along with some water until it melts to a softened, vaseline-like consistency (some people call it a mashed potato-like consistency). Then you quickly glop it into your molds before it sets up again, banging the molds real hard to get any air bubbles out, and covering with plastic wrap and weighing it down with a heavy book or something (at least that's what I do
).
Some people like to cook the soap gratings in their crock pot; some in their oven on low; some in a double boiler; and some in a pot directly on the stove. I've done them all except for the crockpot method (don't have one for soap). I liked the oven method best. I think I had it set to 150 - 175 degrees F (because the flashpoint of my fragrance that was already in my soap was 200 degrees F).
What I did was put my soap in an oven safe pot with some water sprinkled on the soap, covered it, and cooked it, checking on the soap about every 20 minutes to a half hour and strirring it each time until it was like vaseline (it could take a couple of hours). I also added water to it a teaspoon or more at a time if it was looking too dry. You don't want to add too much water because the finished soap will be soft and it will warp over time as the excess water evaporates out.
Just so you know, it won't ever become perfectly pourable like CP is perfectly pourable, and it will look more 'rustic' than CP, but rustic is not necessarilly bad at all. I personally like the rustic look of rebatched soap. I think it looks very cool.
As you cook it, it will eventually get soft, mostly smooth with an unmelted soap grating here and there, and vaseline-like. Some people add sugar water to it in order to make it even more smooth, or Sodium Lactate. They say it helps make it less gloppy and more pourable. I haven't tried either of those yet in my rebatches, so I don't know first-hand how well they work, or how much to use. Maybe someone who has will add their wisdom.
Once your soap cools off and sets up again in the mold, you can unmold and use right away. No need to cure it. The very top of the soap may resemble brains or something, but you can trim that off if you like. The rest of the soap should look fine if you got the air bubbles out when molding and you weighted it down right after (at least the rest of mine look fine if I'm careful to do those things).
Well, that's the method I use. Hopefully more people will chime in with their method.
HTH!
IrishLass