The Icognito will definitely not work for the 400 because it doesn't have a personality board, the OS ROMs plug into the main board.
I almost hope this doesnt work for a 400, I'd have to switch my vote for 2... heck, maybe 3 - one spare...
Any similar upgrade for the 400 would need to use the single RAM board slot, with additional cables to the OS ROM sockets.
There is also the issue that the RAM board on the 400 is within the shield without an access panel, so changing a CF card would be a major undertaking unless a slot was made in the shield or some type of extension cable/socket was used. A slot through the shield under the cartridge door and behind the cartridge area, positioned so the card wouldn't interfere with cartridge insertion/removal would probably be the good option for such an upgrade.