This advanced option is system-specific and only meant for administrators.
Set the advanced options XS_PROJECT and XS_FIRM along with XS_SYSTEM to point to the folders Tekla Structures searches for property files. Tekla Structures always saves properties in the current model\attributes folder. You can then copy or move them to XS_FIRM or XS_PROJECT folders if same settings are needed in other models.
Note that you can define one path only, not a list of paths.
Changing an advanced option value in .ini files located outside the model folder does not affect the existing models. You can only update advanced options in the Advanced Options dialog box or in the options.ini file located in model folder; not from an options.ini file located in folders defined for the advanced options XS_FIRM or XS_PROJECT. The .ini files are read also when you open an existing model, but only new advanced options that do not exist in options_model.db or options_drawings.db are inserted, for example, such options that are not yet in the Advanced Options dialog box but have been added in the software.