1995 mustang gt starter kill switch

I am familiar with custom wiring, but not an electrical wizz. So my question refers to the relay diagram of basic passive starter kill. I have labeled the relay's X and Y. And 1 wire labeled A. My questions are: What is the purpose of wire A? When the momentary switch is pressed the circuit from 30 to 87 is made providing voltage to the connector at 30. It seems to me that wire A makes the relay rather pointless as wire A would provide voltage when the momentary switch is pressed. Second Question, Is relay y even needed? Would you not achieve the same result by simply connecting a momentary switch between voltage and the 85 connector of relay X? Also, The kill switch I am hoping to use is actually a two position switch, allowing me to leave the kill switch disabled so I don't have to press a button every time to start it. Example, running to the store, having to stop my car to change a tire. I would like to be able to enable the kill switch when the car is going to be parked for a longer period of time etc. Would this diagram achieve what I am looking to do?

There is a much simpler method. 1 relay needed. 85 to ground via a normal S/Pole switch to be hidden. 86 from ignition 87a from starter switch and 30 to starter. Thats it. Second method, 85 to ground via momentary switch, 86 from ignition, 87 from starter key side and 30 to starter. with the first method you're constantly imobilised, with the second method, you need to press a hidden switch to actually start.