Maybe I wasn't too specific in my post, but the idea is that you'd get a different card from the Coward. This new card would unlock the elevator that leads to the sublevel, from there you can obtain a passcard without having to fight a crowd of enemies at once.
So I had a similar idea which I'm sure you'd really like.
The idea was to add a second Vulkar coward in the sublevel which would be the Twi'lek coward from the vanilla game whilst the Vulkar coward on the ground floor is the human one. The Twi'lek coward in the sublevel would be guarding the heating system generator room whilst the human coward is guarding the Vulkar control room. I say control room as dialogue from the TLK seems to suggest the computer terminal which is found in the main open area near the armory was supposed to be inside the room with the coward NPC:
"I don't know. Maybe you could use the main terminal in this room to override the security system, if you're good with computers. Otherwise you'll need to get your hands on a pass card."- Vulkar Coward
This would suggest that the coward was guarding a control room akin to the one found in the Hidden Bek Base (the one that's famously locked forever in the vanilla game) instead of just some random room as we got in vanilla.
My plan had the Vulkar Lieutenants from the barracks moved to the sublevel so that the barracks would have the passcard in a footlocker guarded by 10 enemies whereas the Lieutenants would have energy shields but would have fewer guards protecting them. By having the Twi'lek coward in the sublevel as an NPC, his dialogue on the Lieutenants still works as there are Lieutenants on the sublevel with him.
I also know there's an option to disable the turrets by disabling them via the computer terminal, but that option is way more expensive then just overriding the power conduit in the barracks (10 spikes VS 3 spikes). I think I might change it so that both disabling the turrets and overriding the power conduit would cost the same, this means you either disable the turrets or override the power conduit to avoid fighting the Vulkars for a Spike fee or you simply attack the Vulkar swarm head on and risk getting killed if you're playing on Impossible difficulty.