first use gimp/photoshop or whatever u use and make the kill marks as u want them, save them as png. then u need to download paint.net link: Download
when u have download and install that open your saved mark u made whit gimp/photoshop and open the original killmark u want to replace just drag and drop the edited killmark and save it tada your done have any questions or problems write them here
Doesnt matter what you use... Just save the edited kill mark as .tga in a different location. Then just back up origianl kill marks and drop edited ones into the CF folder where the kill marks should be