[MT-AU Public] Mangle new routing mark from router traffic

For a long time now I have been steering traffic from the LAN through the router using a <mangle : prerouting : new routing mark> and a routing rule sending that new routing mark out a specific interface. Easy and reliable. Now I want to do the same thing for traffic from the router itself, but it doesn't want to work. It seems the prerouting chain is only for traffic from interfaces, not the router itself, and I can't apply a new routing mark unless it is from the prerouting chain. Catch 22. Am I missing something? Using ROS 6.49.