Can someone remove a Payable of Death off the account if they were not the original owner?

No one other than the owner of the account can change the POD beneficiary.

However, there is a conceivable possibility that a person with a sole account naming a POD beneficiary later added a joint owner to that account. Upon the death of the original owner that account would become the sole property of the surviving joint owner who could then change the POD beneficiary.