i have done what u are trying to do. first i just duplicated the existing shield hardpoint in the cmp file and called it HpShield02, then to make it show in the game u need to change the corresponding entry in shiparch.ini to:

hp_type = hp_elite_shield_special_10, HpShield01, HpShield02
hp_type = hp_elite_shield_special_9, HpShield01, HpShield02
hp_type = hp_elite_shield_special_8, HpShield01, HpShield02
hp_type = hp_elite_shield_special_7, HpShield01, HpShield02
hp_type = hp_elite_shield_special_6, HpShield01, HpShield02
hp_type = hp_elite_shield_special_5, HpShield01, HpShield02
hp_type = hp_elite_shield_special_4, HpShield01, HpShield02
hp_type = hp_elite_shield_special_3, HpShield01, HpShield02
hp_type = hp_elite_shield_special_2, HpShield01, HpShield02
hp_type = hp_elite_shield_special_1, HpShield01, HpShield02

this tells the game to allow 2 shields from lvl 1 to lvl 10 to be mounted.