X19.4 is the right answer however once the Task Order is issued the work involved is added to the Service Information so technically if the Service Manager is only wanting to change the work then either clause X19.4 or clause 14.3 can be used. Seemingly the Service Manager has greater powers under X19.4 as they can issue an instruction changing a Task Order and a Task Order includes much more than just the work as X19.2 also requires the Task Order to include prices, dates, and delay damages.
Despite this, I would stick to giving the instruction under clause X19.4 as it's neater and probably what was intended by the drafters.
Despite this, I would stick to giving the instruction under clause X19.4 as it's neater and probably what was intended by the drafters.