i actually think you should get a stage DQ on any stage u shot wrong equipment, and the option to shoot open the rest of your stages, or to reconfigure gear to meet original division specs and finish match. Either way, stage DQ stands as your score since wrong equipment was used and a DQ for any stages shot prior to discovery of equipment violation.
What might be considered an exception is the circumstance that is probably the most common reason for folks being"bumped to open" the >9 rds at start. Kinda may not fit the "wrong equipment" category. For this particular infraction an added time penalty might be sufficient. (Unless the match calls for a"gun may not excee X capacity" in the rules, which would be an equipment violation and handled as noted above)