When you start RenameSheets, you first get a loading screen. At this point, the tool looks to see which custom properties are present at all. These will be displayed later as choices in a drop-down menu.
To do this, RenameSheets goes to the first model view after the sheet format on each sheet. This is usually the main view from which all other views are derived.
The variables of the properties are read directly from the part (in the configuration as shown).