Yes, you can do this now with Verizon Wireless. If both numbers are on the same account it is easy. Contact Customer Service and request to change whichever line you'd like to the Digital IMEI in your iPhone XS, XS Max or XR. Just helped a friend with this. If they are on different accounts you must have access to the account your requesting to make a change.

Settings > General > About  > Digital SIM IMEI is what Verizon will need to make the change. Upon entering this, their system will auto generate a digital SIM. They will email you a QR code you will need to scan via Settings > Cellular > Add Cellular Plan. Make sure your on iOS 12.1.2 or later.