XThreads input value into global user value

[Lilz]

I see...

I wanted to:

Create any thread where user can reply giving value X for mykey
Value X is visible on user's profile or/and on every that user's postbit near avatar etc.
User can change/overwrite mykey value for that user with new post

I tried before somehow place form with one of custom profile fields in newreply template, but I dont know mybb structure well, so I failed