There is a feature request asking for that: Allow bypassing min post length for certain groups or trust levels. Though I like that there are the same rules for everyone, as moderators act as good examples of how to post on the forum.
There are some ways to add more characters to your post, which you could use as a workaround. For example, adding <FakeHTML> which is only shown in the raw version of the post as you can see here:
By the way, users receive a notification about replies in a topic they have participated in, so there is no need to mention them for that.