The rule for rebuying in a Party rebuy tournament are :

"You can rebuy only when your current chip count is less than or equal to the number of chips you started the tournament with."

I assumed that this is a rule to allow someone to rebuy back into the tournament or replenish their chips after taking an early beat and to stop someone with a healthy chip count from buying an advantage and adding more chips to their stack?

But you may rebuy whenever you're all-in. It doesn't matter how many chips you have. if you move all in during the first hour before the hand is finalized you may rebuy.

Do all the online sites allow this or is Party alone?