You could also make up some fake entries so that if a user modifys the ini then it would "currupt" it if it detected changes. Also make it not so easy for someone to know exactly what to modify ie
To me that means, if Level 1 was completed then you should just need to change Level 2 to 1. Maybe make this a number that people would be able to randomly guess? ie Level2=450 or even tetyUyy=2 instead of Having Level2 in plain sight.
Also maybe throughout the game, make the Ini write a value so that it checks this first and if anything else has been changed then it knows someone has been messing with it.
Check if Level3=1 and Value=G then this is legit. If the Value is something else and Level3=1 then it's been edited.
Just some ideas anyway.