Currently you have to use either a chat command (or macro), data broker, or minimap button to switch between bar configuration and button configuration.

Having either a button on each of the respective windows and/or a separate window that allows switching modes would make it easier to quickly go back and forth, or perhaps a shared mode with different mouse clicks/UI elements to manipulate each.

Yep, this will be part of the GUI rework

The new GUI will not have separate bar and button windows, but one window that holds all the relevant settings