You have to edit the armor, armor addon and then the actual 1/0.nif file for the mesh. For example:
I edited the Bikini bra in TES5edit and changed the "First person flags" from "Body" to "60-Unarmed" When right clicking > edit remember to uncheck the box "body" and then check your desired box.
You can also edit the "weight", "value" and "armor rating" at the very bottom.
To find the correct armor addon just find "armature" on the right where you found the "first person flags" you will see something like "00shittySteelBikiniAA [ARMA:02001D9E]"
Then go into the Armor addon section on the left, find, in my case it was 00shittySteelBikiniAA. On the right change the "first person flags" to the same as you changed the armor item to (60-unarmed in my case.) When right clicking > edit remember to uncheck the box "body" and then check your desired box. Again.
Note the "Female world model" section on the right hand side. That's the nif you want to edit next.
When finished close TES5Edit. (make sure "backup" file is checked.)
To find the nif in MO just find the steel bikini mod, right click, open in explorer. Then:
Mesh > Armor > Shitty > Steel > open the .nif file you noted from "Female world model" (braA.nif in my case either 1 or 0 will do as you need to edit them both.)
Collapse Ninode > NiTriShape (usually the first one just make sure the model is green in the 3d window) > BSDismemberSkinInstance > Block Details (Bottom Section)
Partitions > Partitions > Body part > Double click the value of "body part"
I had no idea what to put here so I just guessed and put the number I used for armor and armor addon (60) and it seemed to work.
Once you have done you can save this nif (overwrite it. After you have made a backup of the original.)
Then do exactly the same for the other 1/0.nif.
Sorry if I explained this badly. If you need any extra help or better explaining with pictures. feel free to PM me. I'll try my best to help.
This could be the wrong way to do it and someone more experienced might know how to do it easier.