You've got to use the ModTools
. They give you all the resources you need to change just about any aspect of the game. The tools come with documentation, and there's also a modding forum called GameToast
that you can explore if you're really lost.
The probable reason that you haven't had much luck using hex editors (although it can be done that way) is that the objects in the game have names like rep_inf_rifleman.odf, com_weap_inf_sniperrifle.odf, and cis_hero_dooku.odf. However, you wouldn't be able to edit the ODF (object definition files) using only a hex editor, which is why I'd recommend the modtools.