Well I’m not sure how everything works in blender, I’ve never used it properly. I’ll try and give what I know about exporting though.
I’ll assume that in order to assign a texture in blender, you need to make a material inside of the program with the actual texture in a diffuse slot.
In 3DSMax, if I was to make and apply a material where the diffuse was called “Worm.Tga” , the .Vmt file for the model for that texture would be “worm.vmt”.
Inside of the .Vmt would be a couple of fields for things like how reflective it is and what other special shaders it uses and whatnot.
Most importantly would be what diffuse texture it references. This texture would be a .vtf file usually in the same place as the .vmt, and it is pretty much the original “worm.Tga” with a different file extension.
If I was to make a model that has multiple textures, I could do the same only slightly different:
If the part of the model that requires a different texture is not attached to another part of the model (as in, two differerent meshes in the scene) I could just make two different materials, one for each of the textures. So one part of the mesh could have “Worm.png” and the other could have “slug.png”.
I would then export all of the bits I wanted as a single model, and the model would therefore need two .vmts, a slug.vmt and a worm.vmt.
If the model is a ragdoll or something that can’t be split up into the parts that use different textures, I’m not entirely sure how it woud work in blender, but in 3DSMax there’s a type of material called “Multi/Sub-object” where it can use multiple Diffuse textures with only 1 material.
Hopefully at least 10 percent of this applies to blender