1. Keep a backup copy of your profile. Just use [Add to List…] in options to add one with the current settings. Could save you a lot of grief down the road.
2. All the custom things rkmcswain described are a snap to add to the next version, unlike that little briefcase in appload that isn't all that reliable anyway.
3. Any time you're about to customize a CUIX file make a copy of it in your support folder (I generally add the month and day like Leon 9-19.CUIX). No bigger disaster than having a CUIX file you've been modifying for years get corrupted without a backup.
My Leon.CUIX has just two tabs with many panels that added in a Workspace to the C3D tabs gives me access to all the functionally of AutoCAD, Map 3D, and over 100 custom commands. Makes upgrading a piece of cake. While I don't modify the C3D Ribbon tabs and panels I add our custom QAT, a few Keyboard Shortcuts, and a lot of Shortcut Menus.