I spent the time 2 days ago to investigate this further. The dealer agreement that I originally bought, although transferable to the next owner was a trade in. So it was a total waste of money imo to by a dealer policy for Tire and Wheel as if I remember correctly it was a $500+ purchase that I lost on the trade in...as I only owned the trailer 11 months and traded it in to the same dealer.
I called GS and asked about trying to extend my dealer Platinum+ agreement to be a "complete" level with tire and wheel. This can't be done since modifications to dealer agreements are not allowed and a new agreement would have to be purchased. The cost $599.
However I was able to purchase a tire and wheel agreement for 5 years that I'm told is transferable to a new owner and/or a new trailer as long as it is a 'like type towable'. This was for $299. Which was purchased.
After this experience, the devil is in the details. It seems like a few of these add on agreements from a dealer are not as flexible as a direct purchased GS agreement and even though branded the same are not the same.