I created my srht account before figuring out I'm trans,
which makes my current username my deadname.
I was digging on old tickets and found a feature request
(meta.sr.ht/118), so I'm pondering if I transfer my data
to another account (as stated in the profile page), I'll
be able to transfer the billing and security data too.
I have no important repos on
it so it's fine losing my old account, just wanted to
know how to proceed once I can't (for now) change my
username.

Sure. Can you reach out to ~sircmpwn/sr.ht-support@lists.sr.ht to start
the process? We will need an email confirming the change from both the
old and new email addresses associated with your account(s).