I have the wartime pilot notes and instructions for the Mustang III and Mustang IV from RAF as well as field manuals for the pilots, nothing mentions carrying both bombs and rockets.
They go into great detail of adding bomb racks, HVAR racks, reloading 50 cal machine guns, taking them out - everything shows either Bombs....or HVar rockets, both manuals DO not say both.
This Manual covers the: P51-D-5, -10, -15, -20, -25, P51-K,-1,-5,,10,-15 from the American Army
And British Model Mustang IV.
This is the manual a mechanic would use to repair/maintain and arm a P-51 Mustang, why does it have no reference to loading both bombs and rockets? Its either one OR the other.
I don't want to sound like a broken record here, but Chalenge you showed no proof what so ever yet of your claim, as I pointed out the only photo's I can find are mustangs in korea with any load that consists of bombs AND rockets.
Pretty sure if I go hunt for korean war material I can probably drum up more photos and information, but I am sticking to strictly WW2 here.