Decal help (altering an Illustrator file)

well I just did a quick google and apparently my osx gimp doesn't agree with *.ai files, not to mention early .ai .
Sorry!
when it comes to roughing edges though, I suggest using a low degree of noise filter - and/or redrawing in on a tablet...

I always use the "roughen" filter on illustrator for this - essentially blow the element up as big as it will go on the canvas and then apply

Effect (in the top menu bar) > Distort & Transform > Roughen