Sadly, no they can't disable it...
..Unless they start over again...take the option off.
Set resume locations..wonder if that would work..instead of starting over..? Although, probably not what you're looking for.
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Unfortunately...It will affect other users monitors. If it appears stretched on yours..It will most likely appear stretched on others. Making the graphics pixel-y..grainy.
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It would be nice if we could allow for the user to pick a wide screen option..If anything..
Asking for custom rez option is a far cry..But wide screen..I would think is doable..But again..I think GM would have to do that..or a plugin..would have to be created.