1. Download the mod and extract the .zip file, you can do this with winrar or 7zip.
2. Go to %localappdata%\Packages\Microsoft.HoganThreshold_8wekyb3d8bbwe\LocalState\GTS\1_11_2929_2_active
3. Drop OverhaulMod.pkg and 1_11_2929_2_file_manifest.xml in the folder you have opened in step 2.
4. Make sure it looks like this.
5. Start Halo Wars 2 and play the mod.
How to remove The mod
All you have to do is to delete the files you added