I had success with this today. 2021 2500 Tradesman. As stated in my previous post, I used part number 68475385AA for the key fob. I used 68362518AA for the tailgate damper. I bought the key fob from Mopar Wholesale Parts. They are local to the Phoenix area, so I was able to pick them up and not pay for shipping. I used Earnhardt Chevrolet in Gilbert to program the key fob and activate the XBM sales code. I left the dealership with remote start and the remote tailgate release as if it was installed from the factory. This includes the option to change the horn with remote start feature in the settings menu on the Uconnect screen.
The hardest part of this was getting a service advisor to understand I didn't need to buy the "kit" to activate remote start. The kit is part number 82215841. It comes with two remotes, a wired hood latch, a wire, some zip ties, and instructions. You would still need to pay a dealership to program the remotes. You would also need to pay a dealership to activate the XBM sales code if you don't plan on using AlphaOBD. I was also told it's on been on backorder for eternity. I tried to explain to several service advisors I didn't need the kit, but they wanted to argue with me instead of just taking my money and letting a technician do the work.
If you're in the Phoenix east valley area, Earnhardt Ram in Gilbert was great in getting this done. They were one of the only dealerships with a service advisor that didn't really question what I was doing. If you're in the west valley, Larry H Miller Ram Avondale seemed to understand this process. They also run Mopar Wholesale Parts. I didn't have them do the programming because I didn't want to drive an hour back for an appointment.