Is there a way to use icons other than the ones that can be chosen from the macro list? I know choosing the question mark will show the icon of the spell/item that is being used.

I'm trying to see if there's a way I can edit the macros textpad in the WoW directory to show icons of items and spells that I do not have.

For the question mark icon, it's INV_Misc_QuestionMark. For Earth Shock, it's Spell_Nature_SkinofEarth. Is there anywhere I could find a complete list of names so I could try it out?