The question appears to be asking how to add a toggle switch as an added "starter disable switch", while wiring in a new"DH relay". If that is the question, then the answer is yes, simply wire a switch in line with either the black wire or the purple with white wire(either small wire).
I had not answered yet, because the OP did not reply with a better explanation of what he wants. The word "kill" normally is associated with shutting off the ignition/engine, but he was asking about the DH relay mod, which is about the starter relay, not the ignition circuit.