Yep thats right the rebels have great depower anyway and the shorter lines will help it feel like a smaller kite. The trick comes from the old c kite days where it was fairly common to alter the line lengths to gain extra range from the kite. Its a lot cheaper than buying a 7m kite so give it a go.
Most people in whyalla are all on 8m kites when it gets above 30kts so shouldnt be a problem on the rebel.
good luck