use strict;
use warnings;

while (<DATA>) {
    if (((/^priority/ .. /^\s*$/) || 0) > 1) {
        s/priority/bandwidth/;
    }
    print;
}


__DATA__
Class control
priority 5
Class voip
priority 30
Class video
priority 40


Class control
priority 10
Class voip
priority 25
Class video
priority 45