Since you left out some detail I'm going to share a zero impact solution if you use HDMI. The usual HDMI splitter would not impact GPU performance. This may or may not apply.
There are some display profile apps to switch display profiles. (English is bad at this.)
https://www.google.com/search?q=windows+display+profile+switcher finds them.
First hit is https://sourceforge.net/projects/monitorswitcher/
The setup, I have a desktop expanded across three monitors. I also have a 4th output for a capture card that is duplicating my primary monitor. This is giving me a performance hit when I'm gaming.
What I would like, what I'm hoping someone can help with is switching between having my 3 expanded displays and the 4th output turned off for 1 setting and just my primary display with the 4th duplicate only. Is there a way for doing this? If it helps the card is a GTX 1070.

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