I am Raygoza and keep contact with mod developers of mods I like, I like to help my offering suggestion and ideas. When it comes to modding I am not good at it, I am only able to change a few things in StarCraft and Homeworld 2.
I made this in Photoshop and I think it is possible, the only thing I did change in the original image was the button area, moving all buttons closer to the the right edge and removing the space between the buttons next to each other but kept the space of the buttons ontop and under each other. (otherwise there would be a big gap)
I personally believe that this is possible when comparing to this guy who actually seem to have added new buttons to the game itself, look at he's video where he shows up some of he's stuff and yopu'll notice two extra button slots which indicates that this is indeed possible.
That mod is called Burning Ground (BG).
Image of BG which has extra button slots
A clip of BG having extra buttons and many more things.