How do I get HA to set the dimmer led indicator brightness on 2477D (so it doesn’t light up the room at night)?
Full Disclosure: I don’t use the Insteon integration.
In Home Assistant, in order to set some parameter to a desired value, the integration must provide a service call for that purpose. In this case the integration is Insteon and, based on a quick review of its documentation, I don’t see any reference to a service call that sets indicator brightness.
Alternatively, if the Insteon integration models the indicator as a dedicated light entity then there’s no need for an integration-specific service call; a light entity comes has its own service calls (including the ability to set brightness). However, if you don’t see an entity corresponding to the indicator then it’s not possible to control it.