Hello,
With nand I assume you mean the NOR flash. There is no scenario in which swapping the nand flash is necessary. The NOR flash holds the boot loader, both in the original situation as well as with Enigma2, Neutrino or TvHeadend. The CPU swap can be avoided by installing a socalled modchip, but this still requires swapping the NOR flash to get the correct boot loader. Swapping NOR flash is very hard in case you have a receiver with glued over flash chips although it can be done. Installing a modchip plus NOR flash swap is offered by several parties on the net for usually a modest fee.
Regards,
Audioniek.