Originally Posted by findark

You retain a Q basis with the original coupon value plus a "sticker" EMD that supports revalidation in the higher cabin. For the purposes of changes, the EMD is severable and not part of the coupon value, so a voluntary change will use the original value and per the terms the EMD is forfeit.

For the purpose of the Polaris upgrade list, historically you did improve your position based on your new class (A), but I think I have heard that this changed recently.