Hi everybody! After a lot of online searching I was unable to find a proper guide on how to modify the resource icons used in your map. It's actually insanely easy!
To change the icon, simply open the data editor:
Open a new tab to the Game UI Data, then type in "icon" in the search bar:
Then edit the paths to your image!
If you want to edit the description of the resources, open the Text Editor (button just to the right of the Data Editor icon - it's a giant A).
Type in UI/Resource in the search bar, and edit to your heart's delight!
Any text in the location "UI/ResourceName#" is what will show up when you hover over the resource icon in-game.