Copying files from one Wii to the other
When copying a file that was created on another Wii the copying will fail with a corresponding message.
"Data was not copied."
Changing anything in the data (not the header, see below) will cause the copying to end with this message. Deleting or adding bytes at the end of the file will also yield this message. A checksum seems to check the integrity of the whole file or at least the data segment, since even changing something in the obviously useless and uninterpreted 64 byte zero segments or in the dead space beyond the plaintext strings in the certificate information will cause the copy process to fail with this message.
The White "?" Box
Every manipulation of the bin-file's header will cause the channel or savegame to appear as a white box with a black question mark inside it in the Wii's SD card manager. The file can still be examined but the name and description are filled with question marks also. Interestingly the file will still appear fine even if all blocks beyond the header are deleted. Only one byte needs to follow the isolated header, possibly to prevent the last byte of the header to be the end of file also. The value of the one byte is of no importance.
File does not appear at all
The file will not appear when its directory is renamed. Combined with the last statement this might mean that the Wii checks only the headers first and either the directoy's name is stored in the header in encrypted form or it is part of the key that is used by the Wii to decrypt the header.