To address the question about changing drivers, this is not commonly done for several reasons. Crossover and bass loading are tailored to the specific drivers as a system. Each driver has its own physical and electrical charactoristics. Sometimes very similar tweeters can be switched out without changing the crossover, but otherwise its not just as easy as swapping one driver for another.
Is it taboo to mod a speaker?
I often read and hear about modifications done to source equipment, amplifiers, DACS, and ocassionally I read about someone doing stuff to the crossover portion of a loudspeaker. I myself plan to have someone modify my Pioneer DVD in a few months. However, I rarely read about anyone modding a loudspeaker by exchanging drivers. I have never heard of anyone exchange or upgrading to driver ABC from drive XYZ. Is it done? Does anyone do this professionally?