Does my macOS app have to run before an extension to be discovered by another app?

I have code which captures a screen shot of all displays, but what I really want is to capture screen shots of all spaces. Can someone point me at how i do this? Thanks!

I am interested in overriding the default find/replace dialog which comes up from the performFindPanelAction method. I want to add additional things you can search for like text color and text style/format. How would I go about doing this?