Look at it like this. Modding in general, they're not going to like. But again, Sony does not care. If it does not effect their profits, they have no care. As... If you burnt games and played them, they lose profits. If you buy a game, and give yourself a billion dollars on it. It doesn't effect them at all. In law wise, you own your save file. Which as, they may not care... But if someone said something like. "This guy modded his save file so he's really good." That can't be held against you in terms of law. You "own" your save file. Although if you mean altering the files on the disc, you do not own the disc, even if you bought it. It's like a bus pass. You may purchase it, but it still says. "If asked, you must return it." basically. So are you soft modding, or hard modding? Soft modding being modifying a save, hard modding being the system. Soft modding is fine, hard modding is not. Also on top of that, they will not literally see you doing this. The only way they get on your case is let's say you went online and like killed everyone in a second. They "report" you. Offline however, it's unnoticed, they don't care. Although, do remember that most burnt games are detectable. So be careful with that.
Knowledge, I mod games on PS3 and Xbox 360.