If the /instruments/create API is called for an instrument that already exists in our system (i.e. has an existing instrument_id, it is treated it as an upsert and an update on the existing instrument is performed. The response to the request will then contain the entry previously_existed: true.
Unit21 selectively ignores upserts if the request is identical to a previous request. The response to any ignored upsert will contain the field ignored: true.
Updates to an instrument's instrument_id are not allowed.