You own the copyright to content that you post, but that doesn’t have anything to do with whether or not someone else has the right to edit the title.
We regularly edit titles here if they don’t make sense or don’t summarise the question properly. We do that because we want people to get the best answers possible, and that won’t happen if people skim a bad title and don’t click through.
You get to make the rules on your own forum, so my only advice is not to behave with malice, and to communicate change if it might cause confusion or distress.