A replacing headsail or spinnaker may be fully set before the old one comes down, but only one mainsail and (except while changing) one spinnaker may be set at a time. Only one spinnaker or whisker pole at a time except when gybing, attached to the foremost mast. Sheeting a sail through anything that pushes the sheet or clew outboard of the hull or deck is prohibited, with exceptions for a whisker pole on a headsail when no spinnaker is set, a regular boom, a self-tacking headsail boom, and a boom sheeted to a bumkin. The Equipment Rules of Sailing define headsail and spinnaker for these purposes.
55.1 Changing Sails
Overlap allowed during a change.
55.2 Spinnaker Poles; Whisker Poles
One at a time.
55.3 Sheeting Sails
No outriggers, with listed exceptions.
55.4 Headsails and Spinnakers
Equipment Rules definitions apply.