I would guess that the two png files could be recreated with a different font of the letters/numbers/punctuation, but you would have to do an alpha channel and save them as png with the alpha channel. This task is tedious and sometimes frustrating.
I imagine the data files tell the game the locations of each character in the png files probably as pixel bounds. You might be able to avoid a problem if you perfectly replace each old font character with the new font character without any of the new characters being much larger than the old characters. You would still need to be concerned with the alpha channel.