The BSPs that QNX provides often come with more than one buildfile. The buildfile to select as the source for building your custom BSP depends on the features you want to support. For example, in some cases, BSPs that can support the Screen Graphics Subsystem provide a specific buildfile for systems that provide graphics functionality.
The buildfile for your BSP is located in the directory ${BSP_ROOT_DIR}/prebuilt/${PROCESSOR}/boot/build/board.build. For example: /prebuilt/aarch64le/boot/build/dekelsinore-ghost8.build
For full information on modifying buildfiles, see OS Image Buildfiles in the Building Embedded Systems guide.