Oooh I downloaded your hotpant mod when I first started playing! Go ahead and combine the textures if you want, or I can add it to my to-do list (but may take a while) :)

Yes, the green scientist suit would then turn into the fancy flight suit for all characters wearing it. You can replace Shep’s leather dress but you would have to also replace Shepard’s leather dress mesh with the scientist mesh as well as recode the .tpf file for the leather dress rather than the scientist outfit. It can be kind of tedious – to be fair, I haven’t seen a lot of NPC’s wearing the green scientist dress in the game, so I never really found it a problem :)

It’s because the TPF replaces one of the alternate scientist suits – you need to use Mother of All Mods coalesced edit to unlock that scientist suit in the wardrobe :)