I'm sorry you had such a to-do with the vets again. Poor Boris, I don't blame the little guy for getting fed up! I agree that the stronger they get, the stroppier they tend to get. Obviously a sudden change in temperament, especially if it ties in with a recent treatment, is a concern as you unfortunately discovered. In general they get a bit more normal with each step to recovery, and although it makes it harder for the people caring for the piggie, it's usually a good sign.
I hope Boris stays strong and we see him in a few weeks times recovering to full health and happiness!
Re: the vets. If the vet is willing, encourage him to learn as much as possible! If he can get his knowledge and experience up to a high standard, not only does that help the piggies he sees and treats, but he'd be able to advise other vets in a situation like yours.