Since on the top, the "please PM ___ to change your thread title is gone" I assumed that now you can change it yourself. But I can't, or am I missing something?
Also, why is or was changing thread titles disabled?
And who do I PM to change my thread title if no one can yet?

You can do it yourself now.
If you click to edit the first post of your thread, click on "Go Advanced" and then change it there.
Or in the maini thread index (where the list of all the thread titles is) you can double-click on the empty space directly to the right of your title and it will change into a box where you can edit the title.

Ok, thank you very much for guiding me in that xD

Glad to help. Locking this up now as answered. :)