Is it possible to change details like the colour used to highlight the arrow which points at the currently selected menu option? The one I have chosen (Faux Widescreen) changes the arrow from one shade of grey to another close shade of grey and I would like to change the 'highlight' colour to make this more obvious.
One can edit the Menu Sets (the way that PrE handles the semi-automatic authoring navigation), but I would suggest that you do so with Copies, and then add a folder for those customized Menus. Note the aspects, like the PNG's, which are the thumbnails that you see in Edit Menus.
I would not alter the regular Menu Sets permanently, especially as things can go wrong. PSE, or PS, can do this fine. Just study the full layout of the folders, and duplicate that, in your new folder.