I need help with modifying the .Exe file to support the new dual-screen resolution.

Here's what's bad about not using an .exe: it makes it much harder to track down which register the ceiling value for buildings is being read from, as 127 is stored in many different registers... try increasing the value in the .xml file to 255 or 256 – that way, if the .exe crashes, you can examine the log to see what happened!