Is there any way of using kotor tool to change the character classes? I mean like making non-jedi characters jedi.

hmmm. i think it would be possible.

i hex-edited savegames to make characters jedi. so i am pretty sure you can change character classes with other tools as well.

here is a thread where this is somewhat discussed, though it involves the use of the gff editor and the erf editor, and still focuses on editing a savegame.

http://www.lucasforums.com/showthread.php?s=&threadid=121036)

here's another thread, but once again does not involve kotor tool:

http://www.lucasforums.com/showthread.php?s=&threadid=121039)

i am not sure where your npc class info is stored otherwise, that may allow you to edit it with kotor tool. i will look into it.