You are right MVPs have to pick a posting char and stick to that, with rare exceptions. It used to be that once you were flagged green, every single Blizzard forum showed you as green and you could not change it. All chars too.
The forum software changed in 2018. Permissions for the WoW forums are now set by the groups you belong to which are handled at the Character level. A character can be part of more than one group such as being part of Trust Level 0, 1, 2, and 3. Being part of various Beta groups that grants posting access, etc.
Some things such as titles and text color are also set there. They switched me to the CC group for posting permissions but I am still a CS/TS, WoW, etc MVP.
I THINK to fix it they are going to have to make a custom group for anyone who is both CC and MVP to keep the text green and fix the title to show both. I would gather that is not a priority right now for the forum software folks.
Yes, or on the relevant sub forum. That is really the only means to have direct input. It is also a means for any CC members who are interested in that topic to discuss it with you. It might improve the quality of GD if people actually did that and gave constructive feedback instead of just derailing threads or attacking people.
It is not ideal, but start with that and if it gets to be a major issue I can talk to the CMs about getting a sub forum set up maybe.