I think it not yet exists in HDRLS, but having a symmetry/mirror option would be a timesaving feature to have. The idea is to create a light, and automatically have it and it's properties mirrored at the other side. This would be especially useful when lighting a front or rear image of a product that is symmetrical such as a car or most products.
I really like this idea. Would also be handy to have a multiplier for the brightness of the mirrored content, as you may want it to be symmetrical, but one side brighter or darker than the other. You could also mirror vertically to fake a reflection of the top half of the HDRI map in the bottom half. Thanks for the feature suggestion Steven.