This is where Linux is really good, you can take a raw image of what's on the SD card using the dd command. Once you've got that, you can experiment with the original card in the knowledge that if you make things worse, you can restore the original image and try something different.
First.....
Just for fairness, you can do this on Mac too, you know... same tool...built-in.... dd.
Most people forget / don't know OS X is based on BSD... so anything you can find/do on BSD you can find/do on a Mac. Go discover the Terminal app... therein lines access to the command line.
You can also make an image in the GUI by using the Disk Utility app.
Second....
Your methodology is all wrong.... why are you messing around with the original ?
Take an image, mess around with the image, leave the original intact.