Well, I've heard the opposite. I've heard that you want to be careful what you register because of fusion mechanics later in the game, and how skill inheritance works. And that clean personas are needed in the compendium in some cases.
Any time you register a Persona, if you already have the same Persona in the compendium, the old one will be replaced. So if you find that you need a cleaner Persona registered later on, just replace it.
Hello? Taste? Where are you? This...doesn't taste like anything! This is amazing! It's like I'm eating friggin' water! How is this even...? -Junpei__Iori