Not if you have a multi-line share plan. If you just add a line to an existing family plan, shift your upgrade and then swap then cancel the line, it's not "terminating a contract". Here's the breakdown I found on it.
Steal Another Line’s Upgrade
If you have more than one line on your Verizon account, the easiest way to keep unlimited data is to steal or transfer upgrades between lines and then use the newly purchased phones on your line with the unlimited data. Let me try to explain further, as there are details you don’t want to miss.
If you have multiple lines on an account, Verizon will let you take upgrades and transfer them between lines as long as the transfer is going from phone to phone. For example, my situation looks like this – 3 line account, two have unlimited data, with a third setup as a feature phone that runs me $9.99 per month. Since I keep my phones on a month-to-month status for the most part, I almost always have an upgrade available on one of my two unlimited data lines. So should I want to upgrade one of those two unlimited lines and keep unlimited data, all I need to do is transfer my upgrade over to that feature phone line and use the upgrade for a new smartphone.