MOSQ,
You are right. If the All category is selected and you change P-51B to Attack; then select the Fighter category with the P-51B highlighted, P-51B changes to Fighter. If you then select another plane (P-51D for example) and then re-select the P-51B, scoring changes back to Attack.
I only hope that whatever button -- Fighter or Attack -- is depressed at the time of launch, that is indeed how the sortie will be scored.
MachNix