How about this..
If you are a regular poster and haven't been told off/banned for trolly behaviour you earn a star after a period of time or maybe say after a certain quantity of posts.
Even if you name change you keep the star.
So if you wanted to name change for a sensitive reason or for fun, the star would indicate that you have a credible history on here.
Now, new people could still join in any time of course, but would need to be posting regularly to earn the star (bit like a badge of honour).
We would have to be welcoming and kind to new posters (no hint of being cliquey and leaving them out ) But the lack of a star would clearly show they were new and we could make the effort to be inclusive towards them which would make us come over as more welcoming.
But, if they play up ie trolling they could be identified faster.
Of course this doesn't cover the possibility of a regular poster suddenly turning trollsome, but in such a case we would all at least know it was a regular on here instead of all the wondering if we may or may not have ever had any regular contact on here with that poster.
I'm not saying this is foolproof, but it could go some way to restoring some credibility and confidence.
Just a suggestion. Probably totally unworkable.