I would strongly advise to talk to the service manager. If he/she insists on the original default position, then I would contact the SOA and make it clear that if the merchant does not honor the gold plus contract, you will sue the merchant and the SOA (take detailed notes and record the conversation if no permit registration is allowed in your state – or get permit at the beginning of the call). If that doesn’t work, pay it under protest, make sure you get a dated written receipt that specifically shows the date, description of the repair and that you submitted it under the gold plus warranty claim. I would then take them to small claims court with all the documentation. They would be absolute fools not to honor him.
I don’t remember this “improvement” clause. Good for you to notice. Keep us posted on the outcome.
In what country did this happen and at what dealer?