You have no idea of the magnitude of what you're asking for.
You've seen what happens when oyu move a slider up and down. The associated body parts get stretched or wider of larger, or whatever, and so do clothes.
The thing is, the body and the clothes don't actually look at one another to deform accordingly, each actually has its own behavior, so clothes are made to deform in a way that doesn't clip with the body, but don't need the body itself to do so. They could also be made so that the belly slider instead streches the left sleeve and contracts the right one and the game would see nothing wrong with that.
When you use a body mod with shapekeys the clothes know absolutely nothing about what they're supposed to do, so they do nothing, which means the belly clips through them.
To solve that you'd need to take each individual piece of clothing in the game and design a new behaviour for each shapekey, and that's an absurd amount of work that'd only work for one specific mody mod, because each one has its own shapekeys.
Oh, and it's illegal to share modified 3D models of clothes included in DLC because that's mean you could get them for free.
TL;DR You're gonna have to learn 3D modelling and mod them yourself because a universal solution is impossible.