when did they changed the rule so that you can have a name change only once ?

I think username changes site upgrade was implemented March of 2019, might be able to look that up.

I found out from this user imgflip.com/i/2sg0yo that some usernames with file extensions had a glitch where profiles would return a 404 error, so after name changes were allowed, I changed my name to imgflip.com/user/.jpeg was a good troll.

lol that very interesting and funny