Hypothetical Question!

Your experiment won't damage your equipment, however, I doubt it will reveal much about the cables. First, your listening room would have to be absolutely acoustically symetric. Second, you need to listen in mono. If you use a stereo source the speakers will not have the same input signal. Third, since you are only listening to mono, the cables stereo performance will not be revealed.

In the absence of using a high quality switching box to test cables I believe that your method will work given that sonic differences will be heard if there are various things that remain the same. Ex. - say if your room is square and your speakers are identically positioned from your listening post. I do not forsee any potential damage as a result of this method. I try and do it this way as my sonic memory is probably not as fine tuned as others'. I am more apt to hear differences switching from left to right then trying to remember what something sounds like after I have spent 5 minutes or more changing cables andf replaying a specific song. I am sure that other posters will expand on my position but I think you are on the right track...