You need to do this. Be very clear what you want done and it's to preserve unlimited data. For the first you need to have the rep transfer the upgrade to the basic line, upgrade that line to the new phone (say the note 2), then activated it on that basic line number. Then have the rep move the old phone that was first on the basic line, back then activate the new note 2 on the unlimited data line (can normally use your old sim card but the thunderbolt uses a different size sim card). Make sure they know how important keeping unlimited data is. Should be able to repeat for the other line as well. Don't forget to make sure they cancel any data package that was needed to add to the basic line.
As a side note if cooperate stores aren't willing to help you, especially considering they are all idiots who work there and all they know is how to sell an iphone, you can go to a 3rd party retailer. Tell the 3rd party you want to upgrade but you can't loose unlimited data. Sometimes they will be willing to do this loop hole or even a loop hole of their own to sell you a phone because they make more commission than a cooperate store.
Edit: just read the rest of your post. You won't be able to do this till your upgrade date in Feb. Also you are correct about VZW removing unlimited data. Should they decide to do this and you're out of contract, say you just paid full price for the note 2 then they remove unlimited data, you are royally screwed. But if you do what I posted, anytime you do an alternative upgrade (the VZW term for all for all of this) you resign a contract for 2 years under your old terms. So if you move an upgrade from unlimited you resign the contract for 2 years at those terms. If they decide to drop unlimited data all together before those 2 years are up, it breaks your contract entirely and you are free to walk away with no early termination.