Technically speaking, the Flash storage can be replaced and it can also be upgraded. That said, this is not a trivial undertaking and there are a few caveats to consider. A repair shop that specializes in micro-soldering repairs and has access to a NAND programmer can do this. Depending on the original error (was it Error 4013?), the NAND may just need to be repaired by the programmer. Regardless, all of these options require removing the NAND IC, programming it (or repairing it) and then re-soldering it on the board.
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3