Welp to do this in a basic way you need trx futa armor addon, sense that is not here just dm me and i'll give it to you....

Anyway you need bodyslide and outfit studio, when you open up body slide you need to look in the bottom right corner and click on the thing that says "Outfit studio"

Once in outfit studio go to file ( top left corner} and then click on load project

Choose the clothing you want to load and click open....now you have the clothing in outfit studio

You will now want to click on the top left and click on file again but this time we are going to click on add project

Now find trx futa armor addon and click open

After that its time to be an artist, so in the top left you are going to find a tool increase mesh area, make sure that the clothing you are editing is highlighted(im not talking about the green one in my screenshot)  on the right side

ok so using the increase mesh tool you will hold left click to increase the mesh but before you do that, you will notice two circles, this means if i was to inflate the mesh on one side it will inflate the mesh on the other, depending on what you are editing this can mess up what we are editing, so we are going to turn the mirror effect off

Now the double circle is removed and now we have one

Now begin increasing the mesh( the pantyhose to cover the schlong), some shortcuts to look out for....to increase the size of the circle, hold s and use your scroll wheel to make a circle bigger or smaller, if you mess up hold left ctrl and press z and it will undo what you did

Now lets say it was really hard to see what i was editing, press t and this will disable the texture so you can see what you are editing, press t again to enable the texture again

One last thing to note, if you are trying to edit something and its not working, well most likely that clothing or schlong is not editable sense it doesn't have any vertices to edit, it can also mean that you didn't select the right clothing part on the right side, to see the vertices click on the pencil tool. In the second pic on the right side make sure you selected what you wanted to edit because if you don't you may accidentaly select the schlong

Now if i remember correctly  you can delete the schlong if you want incase if you want to edit it ingame, thats what i did because it worked but you could try to leave it there and see how it goes

Ok lets say you are done and you are satisfied now its time to save, the way how i save is i click on file and I ALWAYS SAVE AS after that a box pops up
i edit the END of the DISPLAY NAME( 1st box), i would put something like (futa) so i can see this in bodyslide, it can be whatever you want though anyway
I edit the END of SLIDER set file before the OSP (4th box)

I edit the END of  SHAPE DATA FOLDER (5th box)

I edit the END of SHAPE DATA FILE just BEFORE the nif(6th box)

Just like the display name i put ( futa) so it works properly

I click save and i exit out of both outfit studio and bodyslide, after that i load bodyslide and i find what i edited and i click build at the bottom and it will show up in game

Now for the erect version. 

Steps are similar but with a few additional steps  but when we add to project we look for trx futanari addon

Now that its added we look to the right and we click on cbbe schlong

After thats clicked on. you click on the bones tab then you go to posing  and when that's done click on npc genitals 01

After that play with the x y z slider to make the schlong curve to your desired way, when you like it click apply to mesh so changes are saved

After that guess what its time for....that's right time to be an artist. But make sure you click on the mesh tab so you can edit the actual outfit. Also make sure you click on the actual outfit so you aren't inflating the schlong mesh, remember from the steps above

When im inflating the dress mesh, im going to exaggerate a bit and add bigger balls  and a thicker schlong like this so i can actually see the erection like this

Anyway for the erect version i delete the cbbe schlong AFTER increasing  the mesh. Look at the steps above to learn how to save again

This tutorial is for cbbe\3ba, but im sure you can do it with unp/bhunp. If you use ube you dont need this as the bulge slider comes implanted already

( DISREGARD THE PICTURE BELOW, IM TRYING TO REMOVE IT BUT IT DOESN'T WANT TO WORK)