Change lightning bolt on/off switch icons?

you can use the custom_control settings available through custom-ui https://github.com/andrey-git/home-assistant-custom-ui/blob/master/docs/features.md#custom-controls

tbh, I havent done that, because I don’t have custom control items available. This doesn’t work with mid incons though.

see here: CustomUI - discussion thread

and a bit further down @andrey 's answer CustomUI - discussion thread