The correct way to do this is to create a new tracking group.
Open the POS Configurator and go to the Reporting tab, Tracking Groups button.
Highlight the tracking group you want to edit, press F5 and then F6. This will copy it and insert a new tracking group in the first available number. Rename the new group so you can tell them apart, I usually use the date, ie. "SYS 2016-11-22"
Make the changes you need to the newly created tracking group.
The best time to make this active is when you run your end of day, this way you won't have any days with partial posting.
To activate it, Open the POS Configurator and go to the Reporting tab, Historical Totals button, Classes tab. This is where the tracking groups are actually linked.
Change the link for any class using the old tracking group to the new one.
Done.
Remember though, this probably won't populate in any reports using a Crystal Reports template. You'll have to add/have someone add, the new tracking line to the reports.