On this platform they allow changing of username once maybe due to the fact that they assigned username and password automatically for quick registration.
I just checked and can confirm that their system allows you to change your username only once. After changing it, the edit button will disappear.
I’ve messaged the OP regarding the $5 offer and provided my original username. I’m not sure if I need to send another PM to inform him about the username change or if I should contact PrecariousPanda instead.
By the way, it’s been more than 24 hours since I sent them my username, but I haven’t received anything yet.