Sorry, there is not such a setting foreseen. You are the first one, I think, with such a request.
The settings are the same since the (pre 2017) releases I started with.
I could modify the dashboard scripts to have rain in inches.
BUT the forecast of WeatherUnderground does not support inches for rain when “h = Hybrid units (UK)” is selected.
There is no way to change the WU forecast texts from mm to inches.
That would result in a mix of units, your rain in inches, forecast from WU in mm.
Also how do I get the Moon Image to display in there MoonPhase box as here https://pwsdashboard.com/pwsWDxx/
Rather than as mine displays
The ongoing work on the svg images => http://discourse.weather-watch.com/p/544990
First post contains updated .svg and the needed .png