After Yosemite, users can’t no more edit .iso files by mounting it to Finder (even hdiutil won't do the job). This blog shows you the easiest way I find so far to edit iso files on Yosemite using no additional software. 

    1. Open Application -> Utilities -> Disk Utility, click New Image, and create a new image using the following setup (change the size to fit your need). It takes ~5 minutes for me to create a 8.3GB image. After it’s done, you will see the new Disk Image mounted in your Finder’s sidebar.

    2.  Now open the .iso file (double click) and copy all the files to the new Disk Image. Now you can do whatever changes you want to the image.