You can launch them with wrottgl with winrottgl's options in the launcher. Select from the drop-down list the alternate .RTL levels and click play. Or you can play them too in regular ROTT with dosbox by running setup.exe, selecting run custom levels and saving and exiting. : )

you have to save and exit to ROTT otherwise ROTT will load darkwar.RTL your save game files will load the correct level set.
ROTT uses two different file formats
RTL files are both comm-bat and single player levels.
RTC files are comm-bat only level files.