The best way to extend Pier's user model?

Hello, I want to give pier users additional attributes (first name, last name, email, etc). So far I was creating a subclass of PUUser. Would it be better to just extend PUUser by a few Magritte descriptions on the class side? When I load new versions of Pier-Unix-Security from Monticello, I guess my additional description methods would be deleted again? And if I put them into my own category *my-customizations (with a star in the name), monticello would leave them alone? And, on a related note, what if I want to change a method in Pier's core (like PULogin class>>isValidIn:), how do I avoid that the next load from monticello gives me that old version again? Cheers Matthias