After adding a JPanel to a JLayeredPane using
layeredPane.add(panel);
After adding this if we change the panel does the panel in the JLayeredPane also change?
Yes. Objects are passed by reference in Java, so any changes you make will effect it.
You may have to repaint the panel after making changes, in order to get it to show up correctly.
After adding this if we change the panel does the panel in the JLayeredPane also change?
Yes is possible, but visible only by calling
layeredPane.add(panel);
layeredPane.revalidate();
layeredPane.repaint();