Let's take as example classic_shorts.iff

- The STATIC mesh....I think it's pretty easy to edit with blender
- The CLOTH mesh...Is the tricky one
You have to take this into consideration.....the 3D model of the short is inside the CLOTH file....it's just a vertex list without faces.
So to edit the workflow is like the one below:
- Backup STATIC .model file
- 3D edit the STATIC model with blender and let's say make it bigger
- Now using HexCmp or a similar software just check differences between original static and 3d edited one

This differences between the two is the 3d vertex list we want to apply to the CLOTH file: so we need to save them into a new file.
Also....the START hex values of the original STATIC model are the same HEX values we need to find on the CLOTH file....same is for END hex values.
Now we just have to open the CLOTH file and look for START / END hex values and "Inject" the new one.
That's all!