Through the 30 years we have been going to WDW there are certain strategies that have worked and in spite of new FP, FP+ and whatever else they come up with still hold true. Rope Drop, Late Night, and riding lesser rides during parades. These seem to be constants over the years. As the FP system evolved there were strategies, some called them hacks that worked. Gathering as many FP's as early as possible while riding rides standby at Rope Drop and accumulating your stack for late afternoon/ evening rides when they were good all day. Then we evolved to hitting you window per Disney and then we got to FP+ and having to book the three in advance. No we have refresh and 30 and 60 day windows. In my estimation the things talked about here are all just strategies to be employed, not hacks. Hacks in my mind are booking a reservation and making FP+ at 60 days then cancelling your resort reservation to stay offsite which was your plan all along. This is harmful in that it fills room reservations that others were honestly seeking. Disney has fixed this. Hacks also include multiple Dinning Reservations and Disney tried to fix that with the CC hold but since the window for cancellation is 24 hours it can still happen.
I guess as I write this it becomes clear to me that the major difference between a strategy and a hack would be does your action potentially cause another guest to not get a FP+ or reservation. In other words does your action potentially cause others harm? If yes HACK, if not strategy.