(1) If you close Extract Pages and reopen it, do you find that the new preset is actually there, or is there really no sign of it?
(2) In what Script Panel folder have you put the script? There are 2. One is the one that is shown when you right click on the “User” folder in InDesign’s Scripts Panel. The other can be found if you right-click on the “Application” folder in the Scripts Panel (and choose reveal in Finder/Explorer). Try putting Extract Pages in Scripts Panel folder in the Applications folder, and see if it works.