It really isn't any hardcore "hacking" all you have to do is extract the lightsaber .uti 's one for each color saber and short, normal, doublebladed, then you just change the properties using the GFF editor in your KotOR Tool put them in the override and your done, but it will take a long time since there are sooo many .uti's
Edit: Since I personally don't like to override the original sabers your best bet would be to make your own lightsaber, you can refer to this post (
http://www.lucasforums.com/showthread.php?s=&threadid=124284) for how to build the saber and then to my post (
http://www.lucasforums.com/showthread.php?s=&threadid=128735) or another one to figure out how to make it upgradeable