I have just tried this technique while attempting to move a file system from one SD Card to another - but not on Pandora I hasten to add but on a Viewsonic ViewPad tablet. However, I do not believe this fact changes the following.
I have identified 2 issues:
1. When I ran the restore command sudo tar -xpjvf myrootfs.tar.bz2 -C /media/devos/ --numeric-owner this resulted in the sd card containing two additonal levels in the directory structure media/devos/ which were not present on the original SD card. The solution would appear to be to use the option --strip=2 as follows:
sudo tar -xpjvf myrootfs.tar.bz2 --strip=2 -C /media/devos/ --numeric-owner
This appears to solve the issue identfied above.
2. The second issue is more complex. I am finding that the SD card that is restored to does not in fact work correctly despite the fact that it superficially appears to have be identical structure and content. The easiest way for me to prove this is to attempt to use the Voice Note application. With the original SD card mounted, recordings are visible. With the restored to SD card mounted no recordings are visible. On viewing the content of the SD card using linux, the recordings are present.
Any suggestions on how to progress would be most welcome and would doubtless help future Pandora users too.