If there is a file open, you can open another "corrupted" file by using Heroic open (ESC o H). I have discovered a very very useful function of this command: open a file which is to high a level for the current FM.
I currently have severe problems with FM-126.96.36.1994: as soon as the file explorer becomes involved, FM quits without further notice (no message, no dump, no sound, no grunt…). See bug FRMAKER-9277.
Hence I could not save my work done in FM-16 to the lower level to continue with FM-15.
I opened the FM-16 file in my text editor and changed the <MakerFile 16.0> at the very beginning of the file to <MakerFile 15.0>. Of course this violates the checksum - hence the file is considered corrupted.
But alas; it can be opened in FM-15 with Heroic Open!
Good save the Queen! - or better: the programmer who had programmed this feature!