Is there a way to create an Alexa smart home group and pre-populate it based on discovered devices, programatically?
Unfortunately you can't tell Alexa about groups in your discovery response.
In the process of discovering devices via Alexa, I'd like to create and pre populate groups with devices. The devices being discovered have data pertaining to which room/group they belong to, so it would only seem natural to group these during discovery. 
Is this something that's possible? I haven't found anything in their documentation to suggest that it is