Quote: so how can i pick up only once of the stains from "blood_smear_01.mat" or others without modifying the .mat file or how do i modify the .mat files (which program)
You would have to open the texture file (should be a .dds file with the same name as the material) with a program like Photoshop or Gimp. There you can cut out the stains you need and save them as a new image (make sure the pixel length and width is a power of 2! 128, 256, 512 or 1024...)
Then you need to create a new material for it. You can probably copy the original stain .mat file and rename it, then open with the material editor. There you simply put in your new texture in the diffuse slot and the specular map (if you have one) in the specular slot, etc....