ALTQ - Queue Assignment With match Rule
For example, splice in queueing on existing configuration
altq on $ext_if priq bandwidth $ext_bw queue { q_pri, q_def }
queue q_pri priority 7
queue q_def priority 1 priq(default)
match out on $ext_if from $int_if:network nat-to ($ext_if) queue (q_def, q_pri)