The texture file that you need to edit is CS767_9_T.dds.

In case you are new to repainting - easiest way I have found to do this is download a free utility called "DXTBMP"...

Open the .dds texture with that program, then save it as a 24-bit bitmap.  Edit the bitmap with a program of your choice and save.  Open the edited bitmap with DXTBMP, then save again as DXT1 .dds texture.  Pop that in your Austrian texture folder, reload FSX and your work should be visible on the aircraft if you have winglets selected.

If you already knew all that, sorry  ;)