I tried to use ShouldAttackKill in a perk, in the Perk Owner section, with the Target as the condition target. I made the perk have to read 0 on that for the perk to apply an "Apply Combat Hit" spell.
Basically if I hit someone and they don't die, the spell effect should be applied to the target. The problem though is that for some reason the spell is getting applied every single time. I've even tried using the console to see what ShouldAttackKill is registering, and when it clearly registers a 1 the spell is still applied.

Could the problem be that the perk itself doesn't do any damage, but just modifies other attacks? So the condition itself is returning 0 in the perl, but 1 when you test in the console.

Or I could be talking rubbish, of course. The trouble is there's no easy way to test what conditions do for cases like this,