This question is related, but not identical, to this one.
Suppose one sets a notebook option like this
SetOptions[EvaluationNotebook[], Foo->Bar];
...and subsequently one wants to unset this option. Just a straightforward undoing of a previous setting, so that the setting of the option is just as it was before the SetOptions command above was issued.
How to do this?
One thing not to do is to make use of Format > Option Inspector.... Avoid at all cost. Either it's totally broken, or it is so counterintuitive that it may as well be broken.
The only solution I have found is to copy the contents of the fouled-up notebook to a fresh notebook, and overwrite the former with the latter; i.e.:
- Ctrl+A (Edit > Select All)
- Ctrl+C (Edit > Copy)
- Ctrl+N (File > New)
- Ctrl+V (Edit > Paste)
- select original notebook
- Ctrl+W (File > Close)
- Ctrl+S (File > Save); overwrite original notebook by saving the notebook created in (3) to the original notebook's path
Of course, it's almost obscene to call this a "solution".
Is there some other way to return a notebook option to the setting it had when it was created?

Inherited. The documentation states that, when you set a value toInherited, "If no explicit setting is given at any level, then a built-in default value is used. " – MarcoB Jun 07 '15 at 19:00CellContext(which I had set toNotebook). BTW,Inheritedseems to do the trick forCellContextat least. I think this would make a suitable answer, if you care to post it. – kjo Jun 07 '15 at 19:11