Mess it up how?
Basically if you break you save in any way; which would seemingly require for you to try and edit your save manually in a text editor.
Those that are on Android seemingly would have no way of messing up their save (unless they had rooted their device or had an app that allowed them to access the ".toa-data" folder and messed up the saves from there in a text editor app).
For the specifics of messing up, it'd be along the lines of removing commas, curly braces or variables from places they're needed (or expected to be).
Also on the topic of what the OP said, the scene's QR code can be scanned with a barcode scanner app (which might not be possible for those playing from an android device; if they're playing from their phone or don't have a secondary device to scan the QR code with).
As an extra here, it's safe to alter your save data if you only mess with the obvious stuff, and still lets you be "OP". Find where it lists your gold, food, talent/skill/magic points, etc, and just adjust those numbers. Keep in mind it'll only list your available points if you actually have some to use! I tend to start a new game, get like, 1 level, and then just not spend my points. Then when I start editing the save it'll have those points listed in the file, and I can just edit them to be like, 10000 points or whatever (same with gold/food). You can also do the same for your stats, though be careful what you set your str stat up to, unless you like getting pounded by wolf girls even when you win the fight against them :P