When transferring credits do I need permission from the "leaving" university?
You should not take the term "transferring credits" so literally -- nothing is taken away from the (at that time) previous university. Instead, you are convincing the new university that you already obtained some parts of the education they are offering (so that it would be a waste of your and their time to do that again), and have the credits to prove it. The new university then awards you the appropriate credits according to their regulations (which might be more or less than the corresponding ones at your old university) based on their trust that you could in principle pass the modules again. The credits at your old university remain (at least for some time), should you decide to switch back.