Once someone tries it and you explain it to them, they'll remember it. They'll tell someone else, and within a couple of weeks, it will be common knowledge that a certain bug has been fixed. And the understanding that this was a flaw, a bug, something that was wrong, and that it has been fixed, will help people accept this change positively.

This is a very optimistic scenario. Having considerable experience communicating within an online gaming community, I dare to say that it is too optimistic.
The conservatism of most Heroes players is an objective and explainable fact. It will still be complicated by the parallel existence of the regular game and the Warlords expansion with the uncorrected quick battle feature.
It would be wiser to introduce it as a separate option and check if this optimism has sufficient grounds.