[Nexus 7 Q&A, Help & Troubleshooting] bftb0:
Ummm, what?

You've got a CM10.1 nightly ROM with a Motley kernel, and you want to know "how do I get the upgrade"?

Upgrade to what, stock 4.2.2? How would that be an upgrade? It's a completely unrelated ROM!

Look, there are ROMs that are just a little too different to be exchanging body parts between. In some cases - for instance a steady progression of closely related ROMs, e.g. CM10.1 nightlies - you can just flash the new ROM over the top of the old without performing any wipes. But I wouldn't ever blindly mix all of /data between a stock and CM ROM.

Overflashing without a wipe will replace /system and the boot image but preserve:

- Market Apps & their data

- Data from (former?) System Apps & frameworks --- but their corresponding app at the same version may not be installed

It's the last bit that is the troublesome part, and it's why I said "steady progression of closely related ROMS". If the ROM being replaced is not a recent ancestor of the new ROM, you could have -

missing system apps (data present but no app for it) -- not too much of a problem

data present for a system app which is version mis-matched with the replacement System App (can be a problem)

Anyway, there are combinations of ROMs which are so far apart from each other, either in their frameworks or versions of Pre-installed apps, or their expectations of settings found in /data that it's just not a good idea to "overflash" one ROM on top of the data from another - there's just too large a chance of developing all sorts of troubles.

In those cases, you need a "completely New ROM" strategy:

- You make a FULL Nandroid backup of the existing ROM and get it stored off of the N7 someplace; this is for disaster recovery. Who knows - you might not like the new stuff, so it will let you go back to exactly where you were.

- You back up only Market Apps and their data from the old ROM; when they get restored, they will certainly match each other. You can use Titanium Backup (for root users) or the Carbon App (for non-root users) for this purpose. Also other** misc. backups.

- You perform a factory reset to wipe /data (excluding /data/media on the N7)

- You flash the new ROM, and boot it as a brand new device, entering your Google Creds

- Market Download (or sideload from prior backups) Titanium Backup or Carbon (depending on what you used)

- Restore your Market Apps and associated data.

- Reboot once. If you get warnings about "UID mismatch", you need to boot into a custom recovery again and run the "fix permissions" option in the custom recovery.

- Tweak or re-do settings as needed.

** there are some things that can be separately backed up with other apps such as SMS/MMS messages, APN settings, Bookmarks, etc. Or, Launcher/Home apps that let you save & restore your homescreen layouts. Feel free to experiment, or look at the TiBu capabilities here.

You can probably get away with overflashing newer ROMs within the same minor release group without wiping data. For instance, near-stock 4.2.1 -> 4.2.2 or 4.2.3, but not something like 4.1.2 -> 4.2.1. Same thing with CM - anything within the 10.1 grouping might be perfectly fine, but you certainly wouldn't want to overflash a CM9 ROM with a CM10 ROM (for example). At some point it is simply the better idea to install a ROM as if it were completely new, and then restore market apps & data back into that ROM.

If you want to try Pure Stock with "your data", go ahead and install it as above: start out as if it were a completely new tablet, and then finish up with TiBu or Carbon to install market apps & data from backup.

** Whether or not to use Google Cloud service to backup/restore "settings" is a good question; it would be nice if it could be restricted to just generic Android settings alone, but it wants to re-install all your market apps as downloads, too. This will exacerbate "UID mismatch" problems, as you will be restoring them from TiBu or Carbon.