Yes, save files are stored as plain text. If you're on Windows they can be found in c:\Users\<username\.solarus\<game>\save<number>.dat. So with Book of Mudora, if you need to edit the first save file, it would be \.solarus\zbom\save1.dat
You'll need to know what exact variable to edit, and at least in my case I didn't name them with descriptive names, so if you need more details feel free to PM me.
