Opie-wan,
Would you be changing your DOS as well, or just the start of terminal leave? From my initial seperations briefing, I got the impression that the only reason Separations cares about one's terminal leave start date was to know when your final outprocessing appointment would be, as well as establish a NLT date to have all of your outprocessing checklist complete. I was briefed to handle terminal leave requests with my commander and Finance.
So let's say, for example, your DOS was 29 Sep, and you had enough leave to start terminal on 11 Aug. Finance would not sign off on that leave until NET 14 days prior to the start of that leave. So if you decided to slip your terminal leave date prior to that time, nobody but your commander would seriously care, and Seperations would just back up your final out briefing.
Now, slipping your DOS entails filling out a whole new AF 780, unless you're slipping it as a part of the "one-time good deal to move DOS to NLT 31 Dec 02" post Stop-Loss. I think you can only slip it 30 days at a time, and your commander has to sign off on it as in the "best interests of the AF."
I hope this helped. If anyone sees any errors, please correct me.
Peace,
DP