Toolbar Editor for SketchUp is a popular third-party extension created by
The interface uses a live preview system. You can: toolbar editor sketchup
The Toolbar Editor is simple, but these advanced tweaks will make you a power user. Toolbar Editor for SketchUp is a popular third-party
If you don't want to use an extension, SketchUp has built-in (but more limited) toolbar management: toolbar editor sketchup