Warcraft 3 campaign game file editing help

[Brydenman88]

Hi guys I'm new at modding and such so please forgive my lack of knowledge. I was hoping someone could give me some advice on how to change minor details in game files. What I want to do sounds simple but I have no clue how to accomplish it. I want to change a characters ability permanently to another ability. Specifically I want to give a character like thrall or the farseer the Charm ability as opposed to the Earthquake ability.
Is this possible? Can it be done without causing serious errors to other game files?
Thanks for any advice you guys can offer.

 

[The Algerien]

This would probably make you unable to play multiplayer. but if you still want to go on with this than you can do this through edititing the .slk files in the latest mpq either the patch or Wa3x one there are tools to edit them here on the hive jut check the tools section.