hey 
i have the problem that when you press the mod key shift sometimes both charges of infernostrike are used directly
can I prevent this somehow? my macro looks like this
/cast [mod:shift,@cursor,nochanneling] Infernostrike
First question you talking about infernal strike from Vengeance Demon Hunter
I personally do not know a way.
I can think of only a couple of options.
1 - you can make it where it is only cast once per target using cast sequence.
/castsequence [mod:shift,@cursor,nochanneling] Infernal strike, izzisaysnomore
2 - You could put that in a macro on a different key so you have direct control
3 - add a different spell in the rotation. so it cast infernal strike and then a different spell to give you time to let go of mod:shift key
/castsequence [mod:shift,@cursor,nochanneling] Infernal strike, sigil of flame
4 - You could keybind a side mouse button to one of your action bars and move that spell to a side mouse button giving you both control of use and placement at the same time.
Maybe someone else will have a better idea and how to do what you are asking, and I can learn something new myself.
Hope that helped a little anyways.