Applying the current IFC Scheme Setup (click “Apply”) will synchronize all changes (name and value type modification, and data mapping) in the IFC Manager and Settings dialogs for properties that already exist.
If a scheme property assigned to an IFC element type (for example IfcWall) is not yet available in the current project, it is not displayed in the IFC management dialogs until one instance of the type has been defined in the model. If you have a new empty project, you can load a scheme and use it as the initial IFC data.
In the IFC management dialogs, scheme data are shown with a checkbox in front of them. This way, it is easy to differentiate them from non-scheme, custom data, which are shown with a red X in front. This also means that scheme properties cannot be deleted in either the Settings dialog or in IFC Manager; you can only set their values here.
If you switch schemes (“Import” a new scheme, or create a new one after using “Clear All Custom Properties”), then those data of the old scheme which already have values assigned yet do not exist in the new scheme will be converted to custom data, and will appear in the IFC management dialog boxes with a red x in front of them (instead of checkbox they had in the old scheme). In other words, there is no loss of IFC data.
In this case, you will find one of the IFC Export Options (in IFC Translation Setup) useful: you can define whether these IFC properties too should be exported (“All properties”), or just those which belong to the current scheme (“Current Scheme properties only”).