Scawein,
Hmmm....Let's see....so the D-spec calls for a tightly controlled system to allow Tx activation based upon first authorization and then followed by subsequent validation by an independent system. Great idea!!!

I do systems that achieve that goal....in the Grand Cherokee,
Dodge durango....LH...NS..GS...JA...JX Blah Blah Blah. As for the Cadillac XLR and corvette, substitute the "Tx" in the statement above for "vehicle entry and engine start" and you will see how what I work on almost everyday parallels your concept. And yes, there is a way to achieve the goals of your idea without modifing transmitters.

For specifics, Just PM me

Mark