It seems not possible to change the environment and/or the puppet master to "inherit from host group" via the API for an existing host.

• environment_id = nil or '' -> says {"environment_id":["can't be blank"]},"full_messages":["Environment can't be blank"]
• environment_name = "inherit" -> {"message":"Could not find environment with name: inherit"}

(I always specified a valid hostgroup_id)

It does work with Operating system etc. by setting those to "" (eg "operatingsystem_id"=>""); those are then reset to the ones specified by the hostgroup.

I tried to go through the code, but the API is a bit opaque for me ...