Can you go pistol grip on a shotgun? As already answered yes. Should you? That depends really.
If you plan on shooting your shotgun any decent amount that pistol grip isn't going to be fun. Even if you throw on a collapsable stock it's not going to be even a tenth as nice to shoot as one with a regular stock on it. If you don't plan on shooting it much and are doing it more for fun go ahead I guess.