I cant find the reference to suspending weight off the rigging.Currently rule 49 "Crew Position"
I think that's an older photo and this rule is one of the favorites to be re-written. Crew can't be in any position outside the lifelines, sails not to be sheeted outside the lifelines other than by a legal spar, unless specified by class rules (ie boats with a trapeze) crew cannot suspend their weight from the rigging.
At one point it was the fashion on Great Lakes J-24s to roll tack by having the bow & mast man swing outboard from the shrouds, the argument was made that they were only doing it momentarily and it was to "aid steering." I am not fond of J-24s anyway and this struck me as very dubious, did it anyway because you had to to not get buried on the first beat. Some time in the early 90s about 5 or 6 top J-24s got DSQ'd in one of the big races for it.