I am using the CS5 SDK to create new panels and menus for InDesign.
I would like to know if there is a way to modify InDesign's existing native panels and menues. For example, I might want to display additional information about assets in a Library panel.
Sorry, no direct way. You could theoretically build your own panel and then supercede the menu for ID's panel. Nobody's tried it that I know of; and, frankly, I wouldn't recommend it as it could easily break something in ID.