Edit existing watchface

I received my first smartwatch today and I’m looking for a good watchface. Most existing ones that include the weather show it in °F it seems. At least I cannot make any use of that number. Changing it to °C doesn’t seem to be an option. So I tried to edit an existing face to fix that. But “inspect mode” doesn’t work properly. It allows me to select items and warns about editing them but doesn’t provide any properties to edit. I’ve played with creating a new face before so I know there’s more to the editor than what is shown.

Is there any way to customise an existing watchface and build my own based on that? Or will I have to create my own face all from scratch? (Eventually I’m going to code it without Facer because I want features not supported, but for now I’m trying to get along with minimal effort.)