As for price reductions, some exchanges allow reductions, others model them as cancel + order but allow the new order to take up the priority of the old order (effectively a reduction) and still others model them as reductions, but you still lose priority (effectively a cancel and new order). That is largely immaterial though, because even if you allow reductions, if a large order hits a level it clears fully through that level before anyone can make any reductions. In fact, reductions aren't a problem, increases are because it would allow someone to sit in front of the priority queue until a level is fully cleared.
Something that did happen on some exchanges, which is closer to what you are getting at, is that on some exchanges the fill feed is less latent than the market feed. That is you would get notified that an order executed before that order was disseminated on the order book. This would allow you faster insight into the market, so people did use sentinel orders for that, but if a single order was hitting a level enough to clear it those sentinel orders wouldn't help you get out of the way on existing orders at that level, they would get filled as well. But it could be a leading indicator of multi-level sweeps. Largely that wasn't desired functionality on the exchanges side, just a by product of their architectures, but people whose job it is to understand how the exchange behaves, clearly had advantages there over those whose job is not that.