Inside the program, by changing the source code.doxlulzem wrote:I know I sound like a reeeaaalllll noob, but where do you put the .diff, and will it change the level crossings in existing savegames?
The common name for .diff file is "patch", as in a "source code patch" in this case, which is explained at http://wiki.openttd.org/Patch
All games that you load or play with the new version will be affected. I don't know whether you can save a game in the modified version, and later continue playing with that save in a normal version.