You can't set it back to 0, but you can set the kill score back to 0. But kill score dosen't work by 1, it works with the score you make by killing a unit, like a ling give 50 point, zealot gives 200 or something like that, and it goes on... I think the is a list somewhere around this site. I'll try finding it, or you can look around in tutorial database or something like that. To answer your question exacly,
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just asking of something like THIS is possible... kills conditions/actions
No