Okey
I make on "firewall objects" on tab "CIDR subnets" new rule called "bluenet" , network "192.168.0.1/24".
Next i open ssh and execute: db tc set "cidr;bluenet" ip Description "Low priority blue net" Priority 3 signal-event firewall-adjust
When i go to "traffic shapping" to "address rules" tab i see:
Address: CIDR network bluenet
Priority: Low
Description: Low priority bluenet
and i can now manually change prioryty by EDIT button: Low, Medium, High
Nice work 
but i dont know how to check if it works?