Depending on what properties you are changing, the files that you are looking for are located in the "ArchiCAD Library 8.1\List Templates 8.1\Property Data 8.1" folders. The information is stored in "TXT" files named according to property group.
At least this is the case for the US version on Windows.
If you are substantially modifying the database I would suggest making duplicates of the originals and naming the new files uniquely in order to distinguish your settings from the originals. This also allows you to easily do what you are asking.
David Larrew, AIA, GDLA, GSRC
Architectural Technology Specialist
a r c h i S O L U T I O N S
WIN7-10/ OSX 10.15.7
AC 5.1-25 USA