P81 - Hard to hit. This states that shots against flyer are all snap shots unless the model or weapon has the skyfire special rule.
ie skyfire special rule means that the shots against flyers are not longer snap shots, but "normal" shots.
P42 - definition of skyfire. Nowhere in this definition does it specifically state that this changes the shot from a snapshot to a "normal" shot, but we know it is changed because P81 tells us that skyfire DOES change it from a snap shot to a "normal" shot. Therefore, the only thing that causes the shot not to be snapshot is by changing the BS.
This is backed up by P13 by the definition of snap shots, which tells us that for all snap shots the BS is counted as being 1. Now you have modified the BS - it is no longer a snap shot.
All snap shots are BS 1, but not all BS1 shots are snap shots - you aren't firing snap shots just because you are BS1, you could just be a crap shot.
This is again backed up by the psychic power foreboding, which needs to tell you that weapons that can't normally fire overwatch aren't allowed to fire. Why? Because changing the BS means they are no longer snap shots.
The wording for POTMS is the same in meaning as for Skyfire in that it changes the BS. By changing the BS it is no longer a snap shot and you can fire your template.