How can I modify a DVD image (ISO) and then burn a new DVD?
I know of two techniques to modify readonly disk images - using either a sparse image or a shadow file.  Here is what to do using a shadow file:

Create an image of your cdr (which you have already done)- I will call this xxx.cdr.

Use hdiutil attach xxx.cdr -shadow which mounts the read-only xxx.cdr image along with a shadow file where all changes will kept.  So it behaves like a mounted read/write image.

Make your changes.

Unmount the disk - you will now have xxx.cdr and xxx.cdr.shadow

Now run:

hdiutil convert -format UDTO -o newxxx.cdr xxx.cdr -shadow


Then burn the newxxx.cdr to `DVD-R.

This is the method I have used to create a Snow Leopard image for use by Parallels or VMware. My posting in a MacRumors Thread is just part of a long discussion.  

You may need to vary the above to suit your particular needs - I have no direct experience of working with PS2 images.