Well, in order to save multiple games into a single data file you'd almost have to use memblocks to store the data, for only in memblocks can you extend the data used by the current file. (Get file size, make a memblock that is larger, read the file to the memblock, add the new game save, save file--and so on.) Memblocks also read-write access to the data contained in them, something you can't do with your basic file access. The other way is to make memblock from file, close the file, delete the save file, write memblock to file, write the new save game data, then close the file.
Either way, you have to do the act of "blocking and deblocking" the saved data yourself, using the memblock commands to retore, save or delete the saved data. The other way is to make two files, an "input" of saved data and an "output" of new saved data, which can be at least as complex as using a memblock. (And then you must test for both versions of the file, which must be deleted and rewritten at each save. Like I say, memblocks are easier in this regard.)
good luck!
S.
Any truly great code should be indisguishable from magic.