Serial API 2.0 question for custom code

[ieris]

Hello,
I'm creating a custom project and want it to be compatible with MySensors API.
I have a following situation and do not understood what would be the correct way of communication between gateway and node:
Node-0 <-gateway
Node-1 <-temp sensor
...
Node-10 <-temp sensor
Node-50 <-relay node

Temperature nodes are sending data to gateway and relay node.
By example relay node are receiving temperature from Node-9:
9;2;1;1;0;21.60

I want to send a 'set point' temperature from gateway to relay node, how this message should look like?
0;9;1;1;45;22.00 ? (V_HVAC_SETPOINT_HEAT=45)
Is it ok to send a temperature node-id in child-sendor-id place?