This changes comes into effect from Twilight Summer Series Race 1 (2015).
Sailing Instruction 25 Special Regulations
Part e becomes
(i) In Saturday racing, MPS spinnakers are allowable, i.e. a spinnaker may be set without a pole.
(ii) In GFS Twilight Series races, only a mainsail and headsails as defined in RRS 50.4 shall be permitted. Headsails shall not be set flying and must be tacked to the foot of a permanent forestay and fully hanked or attached to the permanent forestay by a luff groove device. No sail shall be set forward of the point of attachment of a permanent forestay.
The Sailing Instructions on the Yachts page have been updated to include this change.