Runes of Magic US / AU

I was wondering if there was a way to add custom skill icons to the game. I did some research and for WoW, you can simply add them to your Icons folder in your Interface folder (I tried using tga, png, jpeg, and a couple other formats). I tried that and it didn't seem to do anything.

I also tried using Macroicon which works to the extent of enabling and showing more icons that are already implemented in the game but didn't allow me to add any of my icons to the list (it also misses a lot of icons for items, weapons and skills).

Is there some way to actually add my custom icons to the game for macros or is it something hidden in the game files?