Goto war3viewer and find the blp files for the scorescreen background. Extract, alter, save and upload it into your map under the same file path used in the viewer (ie.e ``textures/glues/scoresceen/bottomleft`` or whatever it is). Hope this helps.
The stat background consists of four files (one for each corner), and theres 5 seperate files for each of the race stat pics (NE,Orc,Human,Undead and generic defeated) Thereis also sperate .blp files for the tabs (i.e. units, rescourses, heroes, ect.) -VGsatomi