depends what you mean with the general case.

Do you mean ...

• ... [^\g1] with \g1 more than one letter?

This is hypothetical, since even one letter doesn't work.

• ... ( (?! \g1) .)*

This Would disallow a multibyte sequence if the match holds a word.

I.e. like the word "not" to be forbidden to follow

• ... ( (?! \g1) (?! \g2) .)*

Here chaining look-aheads work like AND conditions.

For single bytes, this would be equivalent of [^\g1\g2] (if it was possible)

you might be interested this excellent tutorial

Using Look-ahead and Look-behind