I don't know if rotating will have an effect on a plastic instrument, but there is actually a logical reason why people do it on wooden instruments. The bore changes a bit over time and will no longer be completely round. Rotating it will change the alignment and affect response and resonance. Allan Segal, who makes custom barrels http://www.clarinetconcepts.com/ has some comments about this on his site.
Thanks for quoting me, Clarnut.
The rotation of the barrel works for wooden instruments. I would hope that hard rubber and plastic do not become ovoid. The reurected Chedeville line
now has a barrel (designed by me:mrgreen: and I do not suggest turning it on its axis.HTML: