To be able to read data from the QPPD and write it back to it, you need corresponding data objects on the Workbench. To save some manual maintenance effort, you can generate a set of data objects based on the current customizing.
Generation
The corresponding transaction is /SCT/QP_DOG_VART. The simple selection of a regulation type generates element data objects for all elements of the associated hierarchy, whose name is composed of QPPD element name and value field in each case.
Furthermore, grid tables are generated as a simplified data transfer option for multi-dimensional Object Types.