A simple trick to make plot setups easier is to forego the Page Setup Manager and go directly to the Plot dialogue box and just use the Apply to Layout button to save your page setups.  Easy enough, but what if you need to modify a named plot setup that appears in the top of the plot dialogue box?

This is where the Page Setup Manager dialogue box comes into play.  Right-click on any paper space tab and select Page Setup Manager.  Select the page setup you need to change and pick the Modify button.  Now, just make your necessary changes and pick the OK button and a final pick of the close button in the manager.  You may also set current, rename, or delete page setups by right-clicking on them in the Page Setup Manager.