The WS-2000 and the WS-2902A use the exact same outdoor sensor array. You can save yourself the work and keep the one up on the roof. Only reason for changing it out is if you wanted the newer one at home and put the older one at the campsite. You should be getting up there and doing maintenance every 3 months or at least every 6 months anyway. There is bound to be dirt, leaves, spider webs and insects in the rain gauge so this needs maintenance. I've had my unit for only 6 months and I noticed it started to yellow a bit from sun exposure. So your call if you want to replace it.
If you decide to keep the existing sensor array when you power up the WS-2000 display it will automatically pick-up the existing sensor array. There is nothing to do to get the signal. This is why you can't have two of these at the same location. If you are too close to a neighbor, then both of you can't have an Ambient station as there are no channels to configure. They all work on the same frequency and the console picks up whatever it sees. It is a one way RF signal...just like a radio station. The outdoor sensor has no idea how many display consoles are picking up its signal. Which is why you can have as many displays as you want.
As for how to deal with WU, I would recommend creating a new station ID. No need to create a deparate WU user account if you will be the one to manage both locations. WU lets you have numerous Station IDs at different locations. You'll want to factory reset the WS-2902A so that you don't double report to the same WU Station ID. Then you can enter in your existing WU Station ID into the WS-2000 and it will continue off so that you don't lose any history.
Here is how to factor reset the WS-2902A. Basically press Wind and Pressure at the same time for about 5 seconds.
https://ambientweather.net/help/how-do-i-restore-console-to-factory-default-osprey-series/To create the new campsite station ID you simple click on My Weather Stations from the WU Profile drop-down or click on MyPWS link as both take you to the same place. Then at the bottom of the page you'll see the blue button to create a new station labeled, "Add a New PWS."
For WeatherCloud you pretty much do the same thing. Under Devices you'll find the "+ New" at the top right of the page which will allow you to create a new station ID for the campsite.