1: The installation files simply install the F18.exe into your root folder.
Ok, so it replaces the file.
2: The F18.exe that it installs dose not alter anything in the game except the aspect ratio. Other than that, the game play and every other aspect of the original F18.exe file is exactly the same.
I'm quite concerned about the part that I bolded. Did you base your modifications on the TSHv3.06 executable, or on the original F18.exe? That makes a big difference, and this thread needs to make clear what exactly is going on. I beleive from past discussions that this mod is actually based on the TSHv3.06 executable, which really means that TSHv3.06 is effectively required to use this.