Loading data before CustomEditor

Hi all,

I am trying to write a custom unit editor, so I could customise the unit to be inserted into different levels.

[Problem]

I have already written a class LoadData to load different data from text files and stores them in Config (Singleton class), which is currently only runs during Play. Now I wish to customise them in custom editor and add them to the scene. But since the data is loaded during runtime, they cannot be access in the CustomEditor... I have tried adding [ExecuteInEditMode] in the LoadData class... (Should be wrong?)

 [ExecuteInEditMode]
 public Class LoadDataClass: MonoBehaviour
     void LoadData(){
         Read ( skillsCVS,     ref Config.SKILLS );
         Read ( minionsCVS,     ref Config.MINIONS );
         Read ( heroesCVS,     ref Config.HEROES );
     }

     void Read( TextAsset txtFile, ref List<Unit> list ){
             [Code to read data and add to list] 
     }
 }

Should I shift the data loading code somewhere else? Or is there a better way of doing it? Appreciated if someone could guide me in some way? BTW, I'm a Unity noob, using 4.6.1