I've had that happen to me several times. I usually find out about it when I do my biometric check-in, "You are checked in for flight 1423." That's not my flight number? So I waited until show time (on purpose) and called CRS. They said I had been SUB'd on this new trip due to an equipment change. I asked if I was supposed to be notified that I was in a SUB status and given an opportunity to decline the SUB? "Yeah, you probably are." Good I said, in that case I decline but I am available for DFT (remember it's show time now). They then got a bit huffy and advised me that I should know that all these calls are recorded. I told them I knew that and that they knew that EVERYTHING I WAS SAYING WAS IN ACCORDANCE WITH THE CONTRACT! Got drafted twice that way in the last 12 months (it's good to know your contract!)