I did a quick add/delete of a bogus station and it was successful both times.
A quick read of their FAQ says you create a PWSweather account, log into the web using that account, create a 'station' under that account, and create a API key for that station. Then (untested) probably use the station ID and API key as your PWSweather stanza username and password in weewx.conf
You'd want somebody who's registered a system more recently to pass along today's scoop.