If you've got nwn then you'll be able to do this by scripting.
 First download Lil' jawa KOTOR builder module from Here (
http://www.sith-res.tk/)  
 Go to the script editor in nwntoolset and copy paste this in a new script.
 (seems to be the best way to get a permenent model change) 
 //::k_def_heartbt01 
 /*
 Default heartbeat script
 */
 //:: Created By: Preston Watamaniuk
 //:: Copyright (c) 2002 Bioware Corp.
 //:: Modified By Override367 
 #include "k_inc_switch"
 #include "k_inc_debug" 
 void main()  
 { 
 ExecuteScript("k_ai_master", OBJECT_SELF, KOTOR_DEFAULT_EVENT_ON_HEARTBEAT); 
 /*
 object oEnemy = GetNearestCreature(CREATURE_TYPE_REPUTATION, REPUTATION_TYPE_ENEMY, OBJECT_SELF,1, CREATURE_TYPE_PERCEPTION, PERCEPTION_SEEN); 
 if(!GN_GetSpawnInCondition(SW_FLAG_AI_OFF))
 {
 if(GN_GetSpawnInCondition(SW_FLAG_AMBIENT_ANIMATIO
 NS) || GN_GetSpawnInCondition(SW_FLAG_AMBIENT_ANIMATIONS_
 MOBILE))
 {
 string sWay = "WP_" + GetTag(OBJECT_SELF) + "_01";
 int nSeries = GetLocalNumber(OBJECT_SELF, WALKWAYS_SERIES_NUMBER);
 if(!GetIsObjectValid(GetObjectByTag(sWay)) && nSeries <= 0)
 {
 if(GetCurrentAction(OBJECT_SELF) != ACTION_MOVETOPOINT)
 {
 if(!GN_GetIsFighting(OBJECT_SELF) && !GetIsObjectValid(oEnemy))
 {
 GN_PlayAmbientAnimation();
 }
 }
 }
 }
 }
 if(GN_GetSpawnInCondition(SW_FLAG_EVENT_ON_HEARTBE
 AT))
 {
 SignalEvent(OBJECT_SELF, EventUserDefined(1001)); 
 }
 */ 
 {
 object oPC = GetFirstPC(); 
 ApplyEffectToObject(DURATION_TYPE_PERMANENT, 
 EffectDisguise(DISGUISE_TYPE_P_BASTILLA), oPC);  
 }
 }  
 //::End of Script
 ---------------------------------------------------------------------------------- 
 You'll need this script too (I know theres a much easier way to do this but I dont know how, Maybe someody can expalin it to ya, but this is the only way I know how to do it.) 
 Put this next one in a new script also called k_inc_switch and then save it(this is so you can save the first one)
 ------------------------------------------------------------------------------------ 
 //:: k_inc_switch
 /*
 A simple include defining all of the
 events in the game as constants.
 */
 //:: Created By: Preston Watamaniuk
 //:: Copyright (c) 2002 Bioware Corp. 
 //DEFAULT AI EVENTS
 int KOTOR_DEFAULT_EVENT_ON_HEARTBEAT = 1001;
 int KOTOR_DEFAULT_EVENT_ON_PERCEPTION = 1002;
 int KOTOR_DEFAULT_EVENT_ON_COMBAT_ROUND_END = 1003;
 int KOTOR_DEFAULT_EVENT_ON_DIALOGUE = 1004;
 int KOTOR_DEFAULT_EVENT_ON_ATTACKED = 1005;
 int KOTOR_DEFAULT_EVENT_ON_DAMAGE = 1006;
 int KOTOR_DEFAULT_EVENT_ON_DEATH = 1007;
 int KOTOR_DEFAULT_EVENT_ON_DISTURBED = 1008;
 int KOTOR_DEFAULT_EVENT_ON_BLOCKED = 1009;
 int KOTOR_DEFAULT_EVENT_ON_FORCE_AFFECTED = 1010;
 int KOTOR_DEFAULT_EVENT_ON_GLOBAL_DIALOGUE_END = 1011;
 int KOTOR_DEFAULT_EVENT_ON_PATH_BLOCKED = 1012; 
 //HENCHMEN AI EVENTS
 int KOTOR_HENCH_EVENT_ON_HEARTBEAT = 2001;
 int KOTOR_HENCH_EVENT_ON_PERCEPTION = 2002;
 int KOTOR_HENCH_EVENT_ON_COMBAT_ROUND_END = 2003;
 int KOTOR_HENCH_EVENT_ON_DIALOGUE = 2004;
 int KOTOR_HENCH_EVENT_ON_ATTACKED = 2005;
 int KOTOR_HENCH_EVENT_ON_DAMAGE = 2006;
 int KOTOR_HENCH_EVENT_ON_DEATH = 2007;
 int KOTOR_HENCH_EVENT_ON_DISTURBED = 2008;
 int KOTOR_HENCH_EVENT_ON_BLOCKED = 2009;
 int KOTOR_HENCH_EVENT_ON_FORCE_AFFECTED = 2010;
 int KOTOR_HENCH_EVENT_ON_GLOBAL_DIALOGUE_END = 2011;
 int KOTOR_HENCH_EVENT_ON_PATH_BLOCKED = 2012;
 int KOTOR_HENCH_EVENT_ON_ENTER_5m = 2013;
 int KOTOR_HENCH_EVENT_ON_EXIT_5m = 2014; 
 //MISC AI EVENTS
 int KOTOR_MISC_DETERMINE_COMBAT_ROUND = 3001;
 int KOTOR_MISC_DETERMINE_COMBAT_ROUND_ON_PC = 3002;
 int KOTOR_MISC_DETERMINE_COMBAT_ROUND_ON_INDEX_ZERO = 3003;  
 //::End of Script
 ------------------------------------------------------------------------------------once you compile the first script, go into your nwn/modules.temp0 folder and grab the k_def_heartbt01.nsc file and paste it into your KOTOR/override folder 
 I know this seems complicated and pretty heavy, as I said hopefully someone how actually knows how to script can explain to you how to impliment the change model script into k_def_heartbt01 without having to compile the whole thing.. 
 Best of Luck! 
 -Zhoken.