I'd be reluctant to leave a trigger on a tree I'm trying to swing, manipulation of the hold wood is part of steering it, with a trigger your to far away to get back to the hold wood in time, so your cuts have to be right from the get go...
The diagrams are always kinda tricky to figure out anyway until you sit down and really look at it with a tree you're ready to kill.
As far as conventional vs. humboldt... never tried swinging one with a conventional cut???
Sniping (from what I can gather...) is like taking an extra bit out of your face cut, sort of a third angle, Either in line with the desired fall so the butt can sit down faster or off to one side if you intend to roll it off the stump.
Slipping be it side or back... is just plain scary even when it works right, that involves intentionally making your cuts crooked as sin, and usually having the back cut lower then the face... not for the week kneed...
The bit Owl mentioned is referred to as the "soft dutchmen" really just a swing dutch with extra cuts for extra movement, you could even toss in a siswheel on the off side to get really crazy.
My opinion here (well it all is really...) I figure the dutchmen block is more for when I notice that I screwed up on my gun or there is something on that side I didn't notice before, otherwise I try and use cuts to swing em, blocks take extra time to make... and don't use rocks Odin's blind eye who keeps putting that in books anyway... yer face chunk is just sitting there use it.