Then you can name this script, after changing "tag_of_utc" and "onenter_old", to the onEnter script for your module and then create a copy of the old onEnter script and rename it.
 void main() {
 // Check to see if it has already been spawned
 if(!GetIsObjectValid(GetObjectByTag("tag_of_utc")))
 CreateObject(OBJECT_TYPE_CREATURE, "dan13_deesra", Location(Vector(60.82,46.78,4.92), 0.0)); 
 // Fire old script
 ExecuteScript("onenter_old", OBJECT_SELF);
 } 
 Hope that helps, and it is worth reading through the thread Stream suggested. ;) 
http://www.lucasforums.com/showthread.php?t=143536)