Translating books - what are the rules (if any?)

I'm also of the oppinion that you can do this. If you're honest you just write that the book is a translation with additions.
My point is that translating and glossing are two different things. And that if somebody house rules translation to be able to raise quality, if you yourself could write a better book, "translating" from latin to latin should not give greater benefit than glossing.