Like Zakero said, well met!
I might go so far as to say that consistent formatting is the goal. As such, if a file is touched, it must be reformatted to the new rules (provided that the formatting is automatic–not requiring manual intervention–and doesn’t require much extra effort on the part of the volunteers). Parts of a file can be escaped but must include short-ish comments explaining why that part retains the old formatting (to avoid someone in the future scratching her head wondering why it wasn’t reformatted).
In time, much/most of the source should contain the new formatting. Then a committee can decide whether or not to reformat the remaining sources.