Other than that, I also noticed this post:
We have registered another account back in 2014 named "eXch" which has no posts and was locked due to inactivity, however we still have its password [...]
Maybe the forum administration will consider deleting that account to rename this one.
My suggestion is to contact theymos about this issue, as there are infinitesimal chances for him to see this post inside this thread. Best approach is to send him a PM and explain the situation, then kindly ask to change your name. It does not happen very often but I witnessed a few such changes within last years, so there is hope.
The PM was already sent to theymos.