In the past, one could arrange to get a piece of furniture to the manufacturer and they would put them in for the customer. Now, since Thor/Heartland has purchased DRV Suites, I don't know what they do.
Key question is the size of the desk you want to use. If the desk is not able to be moved in via the normal entry points to the RV, then it would have to be put in by the factory, if they do that. If it is small enough to go through the door(s), then one might be ahead to do the change as an aftermarket modification.
You would need to check with a DRV dealer to see if they could ask if the manufacturer would install the desk for you, but again, if you ever chose to remove it, would it fit through doors?
Terry