As idiotic as it sounds, it really does sound like it's forever.
I didn't want to deal with a human to get Platinum, so I went to the package selection web page and de-selected my existing HD package. Then I hit the review order button. On the page that came up, the old HD packages were gone and the new HD + Platinum package for $10 was the option.
Looks like that is the way to go then for anyone who wants it. Will they charge you a downgrade fee when you remove HD prior to readding it?