soil question

So my plant is half gallon pot with some fox farm soil. How bad would it be to use that soil but put in a gallon pot and use some really good soil from a tomato garden. It has a bunch of bat guano and worm castings, with cow and horse manure and its free. I only have one plant that a friend gave me that he wasn't taking care of. I dont have much in to this grow but i don't want to make it fail just because of this. Thanks

sounds like that would work well, it will probably add lots of nutrients to the old soil, maybe back down to 1/4 strength nutes (if your using em) for a couple days until they get over the transplant