Correct answers
YES, you can. I did exactly that. But I first made the mistake of going to a Verizon affiliate store (I did not know there was a difference at the time), and they could not do it. They sold me a nano sim (blank) for $25 though. Essentially ripped me off. I went online, and located a Verizon operated store. I went there back in mid-December, I explained to the rep. that all I needed was a nano sim that was programmed for my account. She was skeptical, but I assured her, that if she could do that, the phone WOULD work. They didn't then (& may still not) have much, if any experience with the Nexus 6. I explained that it was unlocked, and purchased from Google on the Google Play store, and that all that was required to activate it was the nano sim. She took the phone to a back room, and was gone for about 15 minutes. I'm guessing that while she was gone, she contacted VZW tech support, programmed a sim card, and put it in my phone. As she returned, she turned my phone on, made a test call to another phone, and it worked perfectly. She was still speaking to someone on her phone, telling them she was making a test call, and sounded genuinely & pleasantly surprised when it worked. She handed my N6 back to me, I checked it out , made a test call of my own, and I've been good to go ever since. They did not use the nano sim the franchise store sold me, rather, they installed a new one of their own, and didn't charge me a penny. Not for the sim, or the ativation/service. So yes, a VZW owned and operated store (not a franchise store) should be able to get you up and running. All they have to do is program a sim with your account info. Hope this helps! 
YES, you can. I did exactly that. But I first made the mistake of going to a Verizon affiliate store (I did not know there was a difference at the time), and they could not do it. They sold me a nano sim (blank) for $25 though. Essentially ripped me off. I went online, and located a Verizon operated store. I went there back in mid-December, I explained to the rep. that all I needed was a nano sim that was programmed for my account. She was skeptical, but I assured her, that if she could do that, the phone WOULD work. They didn't then (& may still not) have much, if any experience with the Nexus 6. I explained that it was unlocked, and purchased from Google on the Google Play store, and that all that was required to activate it was the nano sim. She took the phone to a back room, and was gone for about 15 minutes. I'm guessing that while she was gone, she contacted VZW tech support, programmed a sim card, and put it in my phone. As she returned, she turned my phone on, made a test call to another phone, and it worked perfectly. She was still speaking to someone on her phone, telling them she was making a test call, and sounded genuinely & pleasantly surprised when it worked. She handed my N6 back to me, I checked it out , made a test call of my own, and I've been good to go ever since. They did not use the nano sim the franchise store sold me, rather, they installed a new one of their own, and didn't charge me a penny. Not for the sim, or the ativation/service. So yes, a VZW owned and operated store (not a franchise store) should be able to get you up and running. All they have to do is program a sim with your account info. Hope this helps!