Besides the file size limitations, when the calculator receives a file without a valid transfer header, it stores it as a character string. That is, it prepends the 5-nibble prologue for a character string object, followed by the 5-nibble length field, so now you have 5 extra bytes at the beginning of the file.
When the 49g+ stores anything on the SD card, it stores it as a binary transferred file. That is, it prepends an 8-byte binary transfer header HPHP49-X, which is followed by the compiled object itself, starting with it's prologue. Of course, if it's moved back to the 49g+'s memory, the header is discarded. But if you put the card in a PC's card reader, you now have 13 extra bytes at the beginning of the file.
So the 49g+ and its SD card can be used to store arbitrary files of limited size with minor modifications, but it may well make more sense to simply use a USB stick.