I fixed the problem. But in 90% of the changes it had no effect.

I have not used any of the offered options.

It would be a useful tool if Notepad offered the possibilty recover a range of errors in the menu widget.

Thanks for your time and suggestions.

If you did a Replace-in-files operation (you weren’t really specific…) and the file(s) you might want to apply @Claudia-Frank 's Undo technique to are NOT loaded into active editor tab windows, you are out of luck as this will be non-recoverable.

The obvious answer would be to replace the variables with the old value again, but I guess
this isn’t an option, is it?

Another way would be using menu edit->undo, but it might be that you have to do this as many times as it was done to replace it in first place.
In just a case I would record a macro and then use run a macro multiple times feature.

Cheers
Claudia