If I want to save a latex file created by lyx to a floppy etc, do I just replace lyxpage in your answer with the path to the texfile?
Yes, that's right.
The above commands assume that you are in the directory that contains the latex file that you are trying to save.
Otherwise the full path to the filename could be used.
Also, if you want to restore a saved file from the storage device you just reverse the arrow.
i.e.
lyxpage < /mnt/usbstore/lyxpage