If you still have it you could put it in an enclosure. I really don’t think you’ll run into any problems though. You just wouldn’t be able to open service center and update that Traktor on the HDD that you’ve removed.
de-register Traktor using the Service Center (I just delete the serial number and click OK) THEN uninstall THEN put your new hard drive in, install OSX, then Traktor.
you can always just contact NI whenever you need to install on a new machine, i believe you may have as many installations as you like, provided you only have 2 machines running it at one time. ableton is the same way, anytime i have to reinstall windows , or get a new computer, i just email them and they send me a new key.
you can install traktor on as many machines you like but only have 2 running at the same time
if you change hds or get a new laptop NO need to deauthorise or uninstall just do another install
job done
realised this after going though a few laptops in the last few months and messing with partitions spent ages uninstalling ect no need to do that at all