It is possible, but in another way ^^
You have to edit the whole UI for it.. so simply export it with some tool (e.g.: wc3 image extractor) and edit the texture, add your two icons, that you want to have and import it back to your map, change the path to the right and it will replace the old UI.. you don't need to rework the whole UI, it's splitted in many parts so you can edit just one part for it.. oh and depending on the UI you edit (Orc, Human, etc.) you should lockthe race to the related race of the UI.. else someone could choose Nightelf and don't see the icons, because you only edited the human UI..
The third Icon is the Main attribute and the standard one from Wc3, i think you can still using it..
If you're not good at editing, just tell it, and you might find some people doing it for you (maybe I could do it as well), but it shouldn't be a big deal, because i think you'll have some icons in mind, or at least want to use the common ones.. so just copy'n'paste it into the UI and experience with it to get the right positions for it.. gl with it =)