Hi,
a .Var file is only a little more than a .zip file. You can open/unpack it with every zip-tool.
Just copy/unpack the clothing textures to a custom folder (ideally easily accessible from withing VaM) and edit them.
After this, you can open the clothing items and change the textures paths.
Save your own creation as a preset (or it will be reverted after a reboot) and your are fine.
Like always: Don't share your edited textures without asking the original creators for permission.