In the NVidia Control Panel, under Change Resolution Attributes, there is a refresh rate settings option...but I have never seen an "Override" feature that I recall. I even did a search for this is the Help section, but could not find anything relating to what you are asking.
I guess I am nowhere near what you are asking. Sorry, I do not think I know what the feature is, unless you are calling it something that is known as something else officially.
__________________
|