I have a two year line, and an old Edge line. I swap back and forth between the two constantly. However, the website WILL fight you tooth and nail when you go to switch, so your best bet is to activate the device, swap SIMs and if it doesn't automatically activate, call Verizon with the ICCID for both SIMs to swap them. Once the SIMs have been reprogrammed I've been able to swap them out between phones. My current SIM has been in 3 phones thus far.
Edit: I just noticed you have a S5. To be honest, calling customer service with my recommendation of the SIM serials should still work. Leave the original SIMs in the phones, call in and swap. It literally takes 10 minutes.