Yes, as others have said you can upgrade. We will be upgrading ours to annual passes (after we have availed ourselves of the EE morning). I spoke to someone directly at Disney and they confirmed this, though they could not tell me the value of the DL portion of the city pass. They said they would have to scan the ticket to determine what was paid for it before crediting that amount toward our AP's. We too bought our passes through Costco. I don't know when the scan the tickets if it will show that we paid a discount price or not. Either way for us the cost of upgrade and value of the San Diego tickets still works out to be a bargain. However, in your case, as the previous poster mentioned, it may not turn out to be a cost saving pass for you once you upgrade just for a day.