Since 'Reload HEAT' is an action you can order a unit to perform when you're a Tank Platoon Commander, there must be an Action Command for it, I don't know the exact command but I have this 'string' I copied from somewhere, UnOfficial ComRef I think.
STR_ACTION_MAGAZINE Reload %s
It's probably something like
*tankname* Action ["Magazine",SHELL120]
in the Config.CPPs, SHELL class ammo are HE, while HEAT class ammo are AP - but in the game when you want HE you tell it to reload HEAT, confusing!