Apparantly, if you are handy with a knife than the top plastic trim can be removed and turned around. I did try this on my Juwel 180, but it was siliconed far too much to budge without causing damage (in my opinion).
In the end I just cut some new openings on the new back with a jigsaw and let it be. Unless you have got 'jumping' fish then I can not see the problem with leaving the openings on the front. Just stick a reflector on the lights to stop light pollution escaping from the tank and all will be fine. I have had no problems with mine.