My understanding is that you can only earn up to 10 perk points by earning celebrity stars, but I could be wrong. For that reason it's a good idea to plan from the start which perks you want to work towards as you'll need certain perks to unlock others. If you want to change the perks you have, you can of course reset them and refund your points by booking a celebrity cleanse on the phone. You can also complete the 'World Famous Celebrity' aspiration to receive an extra fame point if you haven't already done so.