The rules are clear but the text on the website at the "F16 Class Rule Summary" page is not.
http://www.formula16.org/content/view/18/40/lang,en/

Maybe line in question should read:
"The rig may not be trimmed between start and finish by other means than sheet, downhaul, outhaul, traveller, mast rotation and halyards systems with exception of diamond wire tension."
or something like that.

edit:John beat me to it.