well you could always just download the mod.sys again, and copy / paste those specific lines back in. Thats if you have done any changes to other parts of those files which you want to keep.
If you havent, then just simply paste over with the entire folder.
bit of advice:
Never close your .py files until you are absolutely certain you are satisfied with working changes you have, so this way you can just undo all the specific changes you have done.
That also helps to find any accidents you might have typed in which could cancel a compile, such as off letters, or commas, or brackets etc.