A am going in Tuesday to have my OBC and rear fog activated on my 05 MCS. Do you see any problem with them also activating the cruise control as well if I do not have the switches installed yet, or will this cause some sort of an error etc etc

I am assuming the 05/06 cars are prewired for cruise

 

Won't hurt anything to activate the Cruise at the same time, most likely just save you a buck to do it at the same time as the rear fogs.