Now, it is easy to workaround this: add 10 characters, plus your one-character change, then remove these 10 characters in the next edit for the same post.
But this can hardly be what the designers intended. Instead, my suggestion is to change it to something like on Wikipedia, where you can mark an edit as "minor". Something like this:
Edits must be at least 6 characters, or select the checkbox "Minor, spelling or punctuational correction."
Edits like that will, of course, not count toward the edit-limit (before it becomes Community Wiki).
The suggestion often seen on Meta Stack Overflow is "just edit more in that post". But sometimes the post is just right, and there aren't any other spelling mistakes to correct. Why force a user to change more than necessary, or use an ugly hack?