It's debatable in this case simply because this is a tournament that goes by certain agreed upon rules, and the wording of those rules determine whether something is actually a foul. Whatever is "common practice everywhere" is entirely irrelevant when there are specific rules that the players have agreed upon to participate in the tournament. And in this case, it all boils down to what exactly is meant by a "forward stroke" written in the rules.I'm surprised this is even debatable. This is 100% a foul. You can roll the cue ball around with the ferrule all day long but you can never use the tip to poke at the cue ball like he did. This is common practice everywhere. Absolutely no question.
IMO, what Chang did was a foul per the rules, since what he did with the cue can constitute as a forward stroke. But rewriting the rules for clarification should help.
Another related question is at what point after the CB is placed with BIH does the CB become 'live' and can't be inadvertently touched? For example, what happens if shooter, after placing the CB in position with BIH, accidentally touches the CB with his stick/finger/clothing? Would that be a foul, even if you can still intentionally grab the CB and reposition it?