Custom Classes for customize.yaml?

I don’t think you can do it with customize however you could create a custom component like this one Better looking device tracker

I monitor everything like what you’re trying to achieve I personally use template sensor to get the status and icon I want. You can find examples in my github under packages/system_status and things_status, I also monitor my zigbee devices that are auto discovered and cant be device tracked in the normal methods under packages/xiaomi