Voted yes but...
I'm watching the scripts again and again and, even with all the will of Calradia, i do not see how that would be possible.
The secondary mode was not made to change weapon or item. It only works to alter an item with other stats that you had provided.
Exemple with native throwing axes:
["throwing_axes", "Throwing Axes", [("throwing_axe_a",0)], itp_type_thrown |itp_merchandise|itp_primary|itp_next_item_as_melee,itcf_throw_axe,
490, weight(5)|difficulty(3)|spd_rtng(98) | shoot_speed(18) | thrust_damage(39,cut)|max_ammo(4)|weapon_length(53),imodbits_thrown_minus_heavy ],
["throwing_axes_melee", "Throwing Axe", [("throwing_axe_a",0)], itp_type_one_handed_wpn |itp_primary|itp_bonus_against_shield,itc_scimitar,
490, weight(1)|difficulty(3)|spd_rtng(98) | swing_damage(29,cut)|weapon_length(53),imodbits_thrown_minus_heavy ],
In the first code line, you have the throwing axe. With it, you have the flag "itp_next_item_as_melee"
This flag mean that the next item in the script will be the item that correspond to secondary mode.
This would mean that each arrows would have his secondary mode but it would not be possible to choose another type of existing arrow.
For example, if you have tatar arrows, it will not be possible to switch to bodkin. You can only switch to a secondary mode for tatar arrows.
It is simply impossible to set this flag with another weapon in secondary mode.
Edit: fack, didn't see it was a heavy necro...