Yes, you can change the gain of a BUGLE with 4 resistors. I would not recommend a switch. Are you not getting enough volume right now? What happens when you turn up the volume control to maximum? If this is silly loud, then the CD player is the problem, not the BUGLE.
Keep in mind that for best sonics and minimal distortion, you want a volume control at maximum setting. Less attentuation = better sound.
jh