Making a notebook unsavable, so that I don’t accidentally mess up the code

I have an algorithm in a notebook that I don’t want to change. I used it regularly. I’m afraid I might accidentally modify a parameter. I’d like the notebook to be executable, perhaps editable, but permanently unsaveable. I’ve tried to accomplish this byHowev Preferences>Advanced>OptionsInspector>NotebookOptions>FileOptions>Savable->False. However, it appears that this setting is lost when I quit Mathematica. Is there a way to make it permanent>