Looks like CWOP is supported, but you need to link it to NOAA in order for Rachio to see it:
See steps 8 through 11 here (link)
You have several options with API
0) Do nothing, use CWOP as outlined above.
1) Check your API usage here (link), Weather Underground seems to track usage differently when data is accessed from one station only, you could be well under your 500 / day limit.
2) Just create a second free API key using a different email.
3) Check if Vera Z-Wave supports getting data from PWSweather instead of weather underground (in which case you can simply switch where API key is used).
Check here (link) for a better instructions on how to setup wufyi which has the script running already. You can start using the website without needing to host or reconfigure the script yourself.