Hello there! So basically, i have done the same thing as force camouflage, with some more steps to make everything work. Here is the detailed process if anyone wish to do the same thing.
In K1, the force camouflage feat itself does not do anything and is purely cosmetic. If Juhani can go into stealth, it's because she has got a stealth belt equipped into her creature hide slot. The stealth belts are obviously not equippable on droids in vanilla, but there is a column for this in baseitems.2da (Droid can use, or usertype, something like that). You can put 3 different values in there, 0 so both humans and droids can use the item, 1 so only humans can, and finally 2 so only droids can.
However, i couldnt "just" change this value for the stealth belt, because it would cause the default stealth belts to be equippable on HK/T3 in their shield slots. So what i did is that i copied the Stealth Belt row in baseitems.2da and created a new row dedicated for droids only so it would not affect the default belts.
There is also an annoying limitation that i couldnt get around with K1. In vanilla you cannot select the stealth skill in the GUI. I thought i could fix this by editing the Skills.2DA file, because its possible in there to edit if a class has access to a dedicated skill. However, even after opening the skill to the combat droid class, if you you try to click on Stealth and allocate skill points there with HK, you get a message telling you that droids cannot use Stealth. However, if you specify a higher "recommanded" priority number for Stealth than the other skills, you actually get skill points invested into stealth by clicking "Recommanded" in the GUI.
This was not working really as i wanted it to be. Finally, a character cannot go into stealth if they do not have at the very least 1 point in their Stealth skill (even if they have items that provides them stealth skill point bonus). So basically, i've added 2 skill points into Stealth to HK by default when he joins you, so he is able to use the thing. I've changed his hide items type for his upgrades by the newly created stealth belt row dedicated for droids, and i've made each upgrade increase his stealth skill so there is still a progression. The belts also provide the newly created feat for HK, which is the same as G0-T0 in K2 btw. Purely cosmetic, just like force camouflage, but it tells the player the new passive.
Kinda convoluted, but it works and that's all i wanted
Also, while we are talking about HK and his hidden items...
In K1, I noticed yesterday that HK's unarmed animations were broken (just like T3). He does have 2 unique melee animation, but It's broken because he didnt have a proper "pause" animation and dodge animation inbetween his melee hits. In K2 this has been fixed by Obsidian, the only thing they removed from K1 model is an animation for poison (cohesive, as droids cannot get poisoned in the game). So i've converted K2 model and now HK has got his unarmed animations fully working (same process as T3!). I'm wondering if I should provide HK some dedicated unarmed feats with his upgrades. Seeing this big robot perform kicks is hella terryfying lmao 😄