Well, the game is written in Visual Novel Maker, so if you can find any program that can read those files, you'll see the data of the save game files. I haven't looked myself, so I'm not sure what's actually in them. That makes trying to edit them potentially tricky; it
may be clear what different values within the save file represent, but it may not.
I'm also not familiar with VNM syntax, so I can't really say I'd know what different things are for, even if you showed me in a reply. In addition, having a base save game file and then a header save game file matching it could make this trickier. If the header file is looking for a specific checksum, for instance, you might need a VNM compiler program to save your changes and not cause errors. Anyone with knowledge of VNM, though, might be able to figure it out easily; I just know that I wouldn't be the one you'd want to get direction from. I'm pretty sure I'd screw up your files.