Some owners of ball pythons have witnessed their BP's prefering mice over rats. Other owners like you are able to switch their's to rats. It isn't an addictive thing for a BP as far as eating rats. It is more the BP identifying the rat as food. All BP's have their own "precerences" when it comes to food. Some don't care what is fed to them while others are fickle to the point of size, color, and a single type of prey. Congrats on the change over to a more convenient food source for your BP.