This topic .. "Switching Between DITA-FMx and FM8/9/10/11/12/2015-DITA" .. is a bit out of date. Would be nice to include better details on switching, in particular with current FM versions where you need to restart FM a couple times when switching to default FM-DITA. Also may need to re-set the required structure apps after switching.
Perhaps provide info on using multiple maker.ini files and using a batch file to swap other files?