The customer is asking to add the functionality to update/configure the Proxy Settings using the Toolbox. 

Currently, the "3scale proxy-config" command doesn't have the option to update the Proxy Settings e.g. changing the Credentials Location.

Is it feasible to implement?

The customer worked around the lack of this feature using the Proxy Update API as proposed: 

export SERVICE_ID=$(3scale service show $REMOTE $SERVICE_SYSTEM_NAME -o yaml | grep 'id:' | awk '{ print $2}')
curl -X PATCH "https://$ACCESS_TOKEN@$APIM_ADMIN/admin/api/services/$SERVICE_ID/proxy.xml"
         -d 'credentials_location=headers&auth_app_key=app_key&auth_app_id=app_id' 

The customer is requesting this feature because with the toolbox its possible to manage the service by its system-name, and using the Proxy Update API they need to query the SERVICE_ID beforehand.