Even if the download button is greyed out, the link in the script still works without login or cookies to get the CSV file with the data.
It’s been a unholy mess for WU as the IBM team attempts to dismantle the old WeatherUnderground API and substitute a newer weather.com API. A public relations AND a poorly planned/announced/developed conversion for the API.
The only scripts using the current WU API are for forecasts (WU-forecast.php and cousins). The graphing scripts rely on the CSV download from weatherunderground.com and (according to them) that is not changing in the future. IF someone was using the WU API for data (not forecasts), then those scripts will have to be changed, but AFAIK, the common scripts from Wim and I do not use the WU API for PWS data – only the WU website CSV downloads.