Is there a way to change tags on a banned post?

It would be nice if we can still have access to the metadata even if the post's banned.

You can only edit tags on posts you can see. There's no way around that, you'll just have to ask someone who can see them to edit it for you.

Is there a reason why they're not accessible? To prevent vandalism? Whenever an artist/post gets banned it hides all the metadata and breaks navigation, and not just on post viewing. If you search a banned artist in the query it doesn't even allow you to get to their wiki, and you'll have to go to the artist list to do that.

Well it doesn't usually make sense to be able to edit a post without being able to see it. It also prevents people from removing the loli tag to be able to see level-blocked posts. For banned artists they were locked down even more strictly after the drama in October, presumably to avoid looking even worse and fuelling the fire for longer.