If this was a straight round trip CX/KA redemption, if you redeem two one-ways under one booking, you are entitled to refund of the difference between two one-ways and return miles after the travel has been completed.

But this does not apply where a stopover is involved. Even if all segments are CX (the example I was given was HKG-oTPE-NRT, NRT-HKG is not eligible for refund)