BaseSystem.dmg
, try using Disk Utility to convert the image to a read/write format. Make your mods, and convert it back. This option, of course, is highly tricky, and it’d be difficult to keep the volume bootable.BaseSystem.dmg
to it. You’ll now effectively have two recovery partitions. This new one, though, not being wrapped up in an image, should be free to add files to. It seems like Mac OS X Base System
has all the requisite files for starting up from, all the way down to boot.efi
. You might have to also jump through a few hoops in order to get it bootable, but it should be far more straightforward than using option 1. Once you’ve done that and tested it thoroughly, you could remove the “official” Recovery HD partition.