If you make a change in a file in the editor and save that file, then yes, that file has been changed permanently.
Whether it is reversible depends, but in general the answer is, unfortunately, "No" unless a copy of the file has been made which a user is unlikely to have done.
It's a double-edged sword of the feature that so much of MATLAB is written in MATLAB m-file code; those files are no different than user-created ones. I've often wondered why the install doesn't mark those files as readonly so such mistakes can't happen so easily altho that makes distribution and updates more complicated for TMW.
If it has happened about the only way to recover would be to restore a copy of the function from a distribution but TMW doesn't make that an easy thing to do, either.
I think it is a weakness...
What you need to do is to be VERY careful to not CTRL-S in a system file in the editor but to cancel out and to not automatically reply yes if prompted to save the file if closing the window brings up the prompt. IS A GOOD REASON TO NOT CHECK THE AUTOMATIC "Save changes upon clicking away from a file." You can get some help if also do not check "Automatically delete backup files when the Editor closes" as then there should be a backup copy of the original.
