I cannot imagine a spelling correction that changes at least 6 characters.
Sure you can. Close your eyes, relax, and picture this:
Leety McTxtspk is asking a question on SO. He misspells most words, because that's just the kinda guy he is. Just fixing the multiple spelling problems will easily bring you over 6 characters...
...But he also forgot to format his code. So you do that too, and now get to write both "fixed spelling" and "improved formatting" in the summary, with no reason to worry about the length limit (since you've now changed every single line of the question).
My point is simply this: the 6-char edit minimum isn't intended to discourage spelling corrections, it's intended to discourage incomprehensive edits!
Typo or misplaced apostrophe bothering you? Fine - fix it. But while you're in there, look around - chances are, there is a lot more you could - and should - be doing. Remember, every suggested edit must be reviewed by at least one other person: don't waste their time.