Hello, due to request by ams I wrote this. It's an analog of "bless" command available under OSX rewritten using grub2 fs functions and according to apple specification of hfs+ on-disk format. This command only update the blessed folder on a partition it doesn't change which drive is used for booting. The later will be a separate command. Also you can choose which volume to boot from by holding option key. Syntax:
hfspbless <DIRECTORY> It works only on HFS+ volumes. Also due to the lack of hardware I wasn't unable to test this "in vivo"