Here is a tutorial..
BACKUP YOUR RAILWORKS.EXE - The hex editor will make a copy for you also but just manually back up a copy anyway..
WARNING I AM NOT RESPONSIBLE IF THIS BLOWS UP YOUR COMPUTER!Grab HxD:
http://mh-nexus.de/en/hxd/Run it.
File/Open/ Railworks.exe
Then View/Adapt To Width.
Now scroll down (it's more near the bottom) to find the resolution you need to edit. I have highlighted it here.
Thumbnails: Click for fullsize.

Now, using your mouse pointer highlight a single digit and just type a number when highlight..
DO NOT delete what is there then type.. Again. Just highlight a single digit and replace it while highlighted. You only need to change 3 values here..
It should look like this when done correctly.

Now save it and run Railworks.. If all was done correctly you should see your custom resolution to choose from now.
