You need Photoshop, GIMP, or equivalent for this to work

If you don't already know how to use these programs, I am not responsible.
XCF is for gimp, PSD is for photoshop. Enjoy.

Also when exporting the textures as DDS, always remember to set it to BC3/DXT5, and to generate mipmaps. Prior to exporting, always ensure that you save your work as an XCF, then merge all your visible layers. After doing so, bring the opacity of the final layer to 7-12%. Then merge it to a new empty layer below it. This ensure the DDS saves as a pretty transparent image.

We do this because payday 2 is weird. And this is how it defines its light levels. After you have exported your DDS, change the extension from .DDS to .texture

pd2 uses .texture as the extension, but it is really no different from a .dds
just a choice on their end I guess.