I believe it is the regular dedicated training that acts on the individucal and through time changes them.
It is the job of the teacher to create an environment where that level of training can occur and the end result is not negative. This may require little tweaks on the instructors behalf but lectures on behaviour outside the dojo - surely not.
That does not mean the instructor should remain quiet if someone is truely stepping across the line but one must be very careful about makeing judgements.
The longest lecture I got on behaviour was the week after I returned to Canada. Bitting my tongue again and again as the group was told what is proper and what is not - and of course how the Japanese behave. In Japan there would be the occaisional life lesson - but oh so short.