Customize the 4 default icons of covers

[alexio70]

Hi, when customizing the icons for the covers I get the message: The following attributes are customized from outside of customize.yaml Possibly via a domain, a glob or a different include. In customization there is an option for JSON templating, like:
{"icon":"if (state === 'open') return 'mdi:window-shutter-open'; if (state === 'closed') return 'mdi:window-shutter'; if (state === 'opening') return 'mdi:inbox-arrow-up'; if (state === 'closing') return 'mdi:inbox-arrow-down'; \n"}
But it does not seem to have any affect. With over 20 covers to configure I'd rather not fix this in the Lovelace with custom 'custom:config-template-card' or custom:button-card.

Running on core-2021.11.2; supervisor-2021.10.8;