This would probably not save much CPU (the GUI is definitely not the most consuming part
). However you can choose to close the Late Replies GUI and select presets directly from the plug-in slot if you wish.
Also it is possible to reduce the size of the Late Replies GUI (by minimizing both the pattern and loops sections). You can save it as your user default, and also lock the GUI (lock icon in the toolbar) so that it's kept small even when switching presets.
And you can save your favorite Late Replies configurations as favorite plug-ins so that they appear in the plug-in menu directly (you can instantiate the right delay/reverb with just one click).