I thought of that but figured it shouldn't be that great a variance compared to what you're doing. But here's an even better idea (OK, I'm a near-know-nothing, but it sounds better to me): After you flash back to original system, go to dual-booting. Then you'll have a MMC of the original system. Let's call it MMC-A. Add your applications, etc. but not your config settings. Make a copy of that onto another card -- call that MMC-B. Then you can make your pref.js changes and other tweaks to MMC-B and, for when you want to compare, or start over, just swap out MMC-B, replace it with MMC-A, and reboot.