I wrote a customizer custom component that exposes a service allowing to change customize values programatically.
set_attribute:
description: >
Set or clear persistent attribute of an entity overriding any value set in code.
Note that calling homeassistant.reload_core_config will reset overrides to their yaml state.
fields:
entity_id:
description: Entity ID to set the attribute on.
example: light.patio
attribute:
description: Name of the attribute to set.
example: friendly_name
value:
description: >
(Optional) Value to set. Leave empty to clear set value.
Note that when clearing attribute it will be empty (and not set-by-code) until next entity update.
example: 'My light'
A downside I don’t see how to overcome yet, is that when clearing customize attribute it won’t take an effect until next entity update.