The trial, as far as BOS is concerned, is just another assessment. There's no special rules regarding assessments after trials - I don't have any myself, but I know a number of classes at my school are doing it.
Definitely. I remain set in my ways that doing so is a permissible option and can be selected from the batch of choices about Trial exams. I have a friend at my school in Year 12, and I know that my school DOES NOT engage in such a practice. So yes, indeed, it is up to the respective cultures of individual schooling institutions.