Yeah unfortunately the only way that I know to really make the non-Reforged UI look like in your link... is something that requires "user script" to run. I'm pretty sure that if you put it in a mod to apply to all melee maps, it might make you desync from other people online during play. So, even if maybe if there is a way to make it not desync, it would still take a while to develop.
I'm sure you could remove the outermost parts of the UI, but I think that in the classic graphics mode there would be black bars showing behind it. To get rid of the black bars you need to run custom script.
Maybe you could do it from a preloader script mod, and maybe those aren't network synced. I wonder.