Glad you find them useful. Adding cards to a set, or preferrably making a new set out of them (I'll probably separate the existing fan-made powers from the official ones in the next update) is certainly possible.
If the items in the existing set show up and you don't get an error message, they should be properly installed. You should then be able to click into the fields, add icons by typing in letters according to the legend at the bottom of the window (visible when you move the mouse over the field; 'e' for melee, etc.), or to remove existing ones with backspace or delete.