Seeking verification: How to retain unlimited data on a Verizon family plan.

Scenario:

Line 1: Unlimited Data Smartphone

Line 2: 2GB Data Smartphone

Line 1 is eligible for an upgrade discount, but if I use this, Verizon will force me off unlimited data.

Question: Can I transfer the upgrade discount to line 2, upgrade line 2 to a new smartphone, then switch the new smartphone to Line 1 with unlimited data and using the old smartphone on Line 2, while retaining this unlimited data?