All Ham functions are hookable, but it doesn't mean it's safe to supercede them.
Ham_RemovePlayerItem happens when you strip an item from the player.
Ham_Item_Drop when you drop a weapon (unsure)
Ham_Weapon_RetireWeapon, in Half-Life you will automatically change to a "better weapon", determined by weight, after you ran out of ammo of certain weapons(throwables) thus calling this method.