Sorry to bump up this thread, but I did say I would report back on the upgrade situation...
The CM I spoke to at Guest Services outside AK tried to add days on to my 6-day NE ticket and couldn't without the system removing the NE part. She was off last weekend when the price increase happened, so she didn't know NE tickets were discontinued until I told her, and then she went to speak to someone to confirm what my options were... She confirmed that my ticket was upgradable for any options that are in the system (upgrade to AP, etc.) within 14 days of my ticket's first use. I asked about bridging and she confirmed that the ticket would still be bridged to preserve the discount from purchasing the ticket from
Undercover Tourist, but we would have to pay any difference due to price increases. Since I wasn't looking to upgrade to an AP, I ask for any further details on the discount vs. price increase situation, but she seemed to be an experienced and knowledgeable full-time CM.