Philippe's answer is the right one. In addition, I would say that it is possible to point to a personal directory in which the "properties.txt" file is saved (containing your own list of properties).
Pointing to a different directory than the one in SolidWorks ensures that your file is not overwritten by a clean install or update to your version.
@bskelton: do you complete your properties from this table? If so, you should know that there are much simpler methods and/or utilities to fill in custom properties in a 3D file.
Smartproperties is the utility to have to complete properties.
A little additional response for the property information utility: there is now one that is integrated into Solidworks (see attached screenshot), so it's free.
it may be sufficient compared to the Smartproperties utility which has more possibilities