Using earlier versions of Traktor
This relates to the Windows version of Traktor
Temporarily running an earlier version
When Traktor is upgraded it stores the previous versions' Traktor.exe in a folder called 'Backup'. E.g.
C:\Program Files\Native Instruments\Traktor 2\Backup\
If you have problems with an upgrade and need to run an earlier version, simply go to this folder in Windows explorer and double click the earlier versions .exe. file The previous settings, cue points, etc will also be used as the previous associated Traktor files root directory will be used by by the earlier version .exe (when Traktor is upgraded it also creates a new root directory for the files it uses leaving the old root directory there in case you ever need to use it again – the default location is in "C:\Users\adam\Documents\Native Instruments\Traktor #.#.#\")
Permanently rolling back to an earlier version
This was the advice received from Traktor support:
'fully downgrade' would just mean to take the 2.6.8 file from the backup folder and put it into the install Dir (overwriting the 2.7.3 that is there at the moment).
You can do this manually, or alternatively run the 2.6.8 update again. You can dl the update here: http://www.native-instruments.com/en/support/downloads/updates/
So a safe way to do this is
Rename this file "C:\Program Files\Native Instruments\Traktor 2\Traktor.exe" to say Traktor-REMOVED.exe".
Copy the older Traktor.exe you want to use from its backup folder into the main "C:\Program Files\Native Instruments\Traktor 2\" directory.
You can also rename the currently used root directory "C:\Users\adam\Documents\Native Instruments\Traktor #.#.#\" to say "\Traktor #.#.#-REMOVED\"
Now run Traktor as normal, verify its the older version you want and that all of your old settings etc are there. Then delete the -REMOVED .exe file and if you don't need anything from it also the -REMOVED root directory.
If anything goes wrong you can rename the .exe and root directory back to as they we're before again and then work out what went wrong.