After adding a BSP you can choose to Select Active BSP. You can also choose to Remove BSP the non-active BSP and/or Rename BSP either BSP.
Regardless of whether you added an existing or new BSP, and whether you made other changes, the final step is to click the Update button on the main Library Manager window to commit the changes. This copies the BSP to the application and then it becomes owned by the application. This also updates the application's Makefile.