If you load on a new firmware, and back up the old one, you can always flash it back to the original. There should be no problems on xbl with a properly patched game; however, there are no guarantees, and it is very hit-or-miss. You will NOT have any problems playing your original copies of games online, though. So, I suggest that you use the burned copies off-line and the originals on-line.
So far, updates have not hurt dvd drive firmwares, the updates are done to the xbox's software, not the dvd firmware.