The Trent 1000 radial drive shaft actually takes it's drive from the IP spool on the Trent 1000. This is unique to the Trent 1000. The original design had the drive from the IP, with a clutch that also connected the HP for starting, to meet the quick starting requirements for ANA. This meant that both HP and IP were cranked when starting.
However after testing it was found start performance was just as good when only the IP was spun up at start up, so the clutch was removed as a weight reduction and simplicity measure.
I believe previous comments from RR point out that the issue was found on an engine stripped after a ground test, so these gearboxes are being changed as a precaution, and to allow strip and investigation. Seems very sensible.