changing 1/2 of an award ticket?

question. booked an TATL award ticket in J for 100K. My outbound flight is great, but I just found a better return routing for 100K. My question is can I call delta and have them substitute a different return routing if it's the same number of miles?

I don't want to cancel the award ticket (PM so no fee) because then i'd loose my original routing on the outbound.