Dumping NAND will not mess up the xbox, writing without the CPU key or on a new dash might. The only way to get a lost DVD key is use xell which is for older dashes to get the CPU key to decrypt the kv, which contains region , DVD key etc. You could then change it to something like all f's or 12121... The prob is once you get that far, u might as well jtag it
Cheers, banjaxt