If you can spare the disk space, I've got multiple rFactor installs on my system. Once the base game is installed to say the League subfolder the first time, I copy the rFactor folder for as many installs as I want so I can do things like install new mods that could possibly FUBAR my league install or whatever. Then you can just create a shortcut to the rFactor in each location for whatever flavor you want to run.
D:\Games\rFactor\League\
D:\Games\rFactor\OffRoad\
D:\Games\rFactor\Karting\
D:\Games\rFactor\Test\