Here's an excerpt from the hdiutil(1) man page section on Hybrid images: You run into a similar problem with the hybrid filesystem images that many OS distributions are shipping these days. | Disk Image (r/o) | | Disk Image (r/w) | We can convert a DMG that contains an ISO to be read/write, but the ISO itself can only be read-only: _ _ So you've probably only converted the container to read/write. The DMG's contents are distinct from the DMG container.
Disk images are just containers that emulate a disk.
