The function of the SAP is as you describe, it helps to warm up the cats on a cold start. This is a different function than what EGR does. I'm not sure if any of the hardware for the two systems in shared, as I said earlier I don't know the specifics of the system on the S54. I just saw an earlier post about an EGR delete and it raised my eyebrow. I would be wary of messing with this outside of race applications. I have no idea how FI on a car like yours might play into it either.
http://en.wikipedia.org/wiki/Exhaust_gas_recirculation