How to merge mesh with EA body?

Hi. These textures are just painted on top of the body, there’s no sculpted barrier between the body and the garment. « Touching ea  textures » should be the number one step in the process of learning how to make cc for ts4, so go for it.

If you do not have photoshop, use photopea. It has almost identical features and interface to photoshop, but is free and online, so you don’t even need to install it. You can follow any tutorial for photoshop in photopea and there are thousands of them.
Start by:
1). Creating a recolor.
Example: two/three color item like a hat or a t-shirt
Goal: to learn how to adjust existing colors with Hue/Saturation, how to apply a specific color using blending modes, a few ways of selecting things;
2). Removing the logo or/an an unwanted detail from a shirt, applying your own.
Example: a sweater with a logo;
Goal: to familirize yourself with many ways of removing unwanted details, how to project logos and patterns;
3). Frankentexturing.
Example: two white shirts with different sleeves, you delete sleeves on one and replace with the ones from another
Goal: to learn how to delete an area of the texture, add it from a different garment, blend the difference between the two;
4). Editing the « borders » of the texture (part 1);
Example: making low sitting jeans high sitting
Goal: to learn how to move an area of the texture and fill/blend the different;
5). Editing the « borders » of the texture (part 2);
Example: reshaping the borders of a basic swimsuit to have thinner straps/deeper cleavage/thongs, etc;
Goal: to familiarize yourself with Warp and Liquify tools. Then, optionally, you can re-draw the texture instead of reshaping it (the thongs);
6). Adding transparency
Example: something skintight, then sunglasses 
Goal: to understand how transparency works in ts4 and how to add/modify it

I think that should cover everything there is to know about editing textures for ts4

The beta version of s4s supports blender 3.3, so if you know how to use it, get it.
There’s no difference between 2.79 and 3.3 when it comes to this, though.
Yes, the texture in the uv editor is the same one plugged into the material
To switch to the shader editor, choose Shader editor in Editor type

This is how the material is set up
1 - texture of the skin
2 - material of the skin
3 - texture of the garment
4 - material of the garment
5 - mix shader that combines both into one
6 - output


Also, the materials and textures in blender are not imported in s4s with the blend. You import the textures yourself in the Studio tab, so to follow the suggestions I game about learning how to edit textures you do not need blender at all