TOPIC: Registration Changes

This came up on one of my web sites where there are multiple options that alter the price they pay.

If a user registers for an event and pays with PayPal, then later uses their Registration Records page to change their registration in a way that alters the amount due, what happens if:

a) the new price is less than they originally paid - does clicking "Pay Now" initiate a credit from PayPal?

b) the new price is greater than they originally paid - does clicking "Pay Now" allow them to pay only for the difference between what they already paid and what they owe?

Thanks,

Ernie