Copy the BSP folder (for example, standalone_v4_2) from the Xilinx install area (C:\Xilinx\SDK\2014.4\data\embeddedsw\lib\bsp).
Paste it in a local directory (for example, C:/SDKProject/repo/bsp/).
Edit the standalone.mld file under the BSP's data folder (standalone_v4_2/data) to change the version number of the BSP.
Change OPTION VERSION = 10.1 to your own version number.
This is done to ensure that you can still choose the original BSP when creating projects.
Go to Xilinx Tools> Repositories > New and add the path to your new BSP.
Now, you can create a new BSP using File>New>Board Support Package>Standalone.
In the next window, you can choose your customized BSP: