Question about award ticket refund (Diamond)

I have never taken advantage of the PM/DM perk of free award travel exchanges.

Can you exchange after the outbound? If so, can you change routing?

I am about to book a ticket DTW-X-DTW. If after I travel DTW-X, could I change my return to Y-DTW, or must the routing remain the same?

The resulting open jaw would be a true open jaw (X and Y are much closer than DTW-X or DTW-Y)

Thanks for the advice