Ours are very bright as well. I just turn them off when we head to bed (if we use them at all). I have a flag mount on my pin box and will leave the single white hitch light on to illuminate the flag, but that's it.
I don't think that there is any easy way to determine if the lights are dimmable by looking at them, but they can easily be removed and replaced with a style/color that is, but you would need to trace the wires inside and find a suitable location to mount a dimmer switch in place of the basic on/off switch.
On my Cougar, the front lights have switches on the exterior forward wall under the overhang. I am not sure if a dimmer switch would withstand being exposed to the elements, or if it would have to be relocated into one of the front compartments.