Add MAX line to Cisco voice graphs

I have LibreNMS graphing PRI usage on my routers, however the longer duration graphs show the usage averaged over each interval. I’d like to graph the maximum usage for each interval as well. I checked and the RRD already stores this information (thanks to the default $config['rrd_rra'] value), so it’s just a matter of adding something like the following to html/includes/graphs/device/cisco-iospri.php:

    $rrd_options .= " DEF:MaxUsed=" . $rrd_filename . ":active:MAX ";
    $rrd_options .= " LINE1.25:MaxUsed#f0f000:'PRI Channels max used   ' ";
    $rrd_options .= " GPRINT:MaxUsed:LAST:%3.0lf ";
    $rrd_options .= " GPRINT:MaxUsed:MIN:%3.0lf ";
    $rrd_options .= " GPRINT:MaxUsed:MAX:%3.0lf\l ";

I can imagine there’s other GAUGE RRDs where this might be desirable.