Well, add 14 to a DC every hyper trigger, and you'll have an approximate value for shields. When you use the spell, I assume you set the shields to 0. If you want the dc to be in terms of whole shield points, add 1 to a separate DC for every 256 you accumulate.
I don't understand what you want, but if it's deal 10% of current unit's life, then no. You'd have to detect each and every unit, have their life stored in a DC (hard to do), then modify the DC and respectively modify the HP (also hard to do). The byte offset is 256, ie... 100 HP in game is 25600 in an EUD.
Wiki article on units. Search for Hunter Killer.