Replace tracks with a different type by simply building over them.
Configuration file: manualconvert
Command line: -Ym
If this switch is active, you can convert a piece of track to another type simply by building over it, instead of having to remove it first. Conversion of stations, depots, bridges and tunnels is also done by building a piece of track (not a station, depot etc.) over them.
For depots, if you convert the depot, any vehicles that are in the depot won't be converted. You'll have to replace the engines and wagons manually. You can't attach the old wagons to newly built trains either, because they would be of the wrong train class, and therefore unable to run on the new tracks.
This patch was contributed by Csaba Varga.