Last week I made an award ticket change on the return portion of a ticket. The agent was able to hold the outbound segment.

The return had a stopover and the agent was able to hold the long-haul flight, while giving me options to change the time of the short-haul flight.

So I believe they can hold award inventory while making these minor changes.

In my account, the activity showed as a re-deposit of miles and then a re-issue.