Edit permission: allow only a certain group to edit the (wiki) posts under a particular category

I don’t want to give them permission to make new topics, nor to reply to the existing topics, but I do want to give them permission to edit topics, without adding them to the leader trust level.
What I am basically missing is the ‘edit wiki posts’ permission. This permission would be granted to a certain group for a certain category, just like other permissions.

If we limit who can edit a wiki in a certain category, than we also have to limit who can create new wiki posts, so we would also need a ‘create wiki posts’ permission just to straighten out permissions.