Mid-route changes?
 

Assume a route such as OAK-LAX-MSP-BNA, with OAK-LAX in the evening and LAX-MSP-BNA after midnight.

Once one has arrived LAX, what change options are available-- can one SDC or standby at this point, and to what flights?

Similarly assume OAK-LAX-ATL-BNA, with arrival to ATL early morning.

Once one has arrived ATL, can one SDC or SDS to an ATL-BNA flight later in the day?

The answer is a guarded yes. Since this may allow you to do things not in Delta's self-interest, I'll leave further execution as an exercise for the reader.

yes - one benefit is that often with married segments this allows you to "break" the system in your favor. say you're flying A-B-C and there's K=0 on the married A-C pair but K availability on each individual leg, you could SDC once you get to B.

also sometimes you can add connections (if you warn more MQM) or drop one, etc. however this is all very much YMMV,

More than enough said. YMMV. Been a while since I was a grad student playing this game for miles :). I hope that those of us who are well above MQD or equivalent, are getting more leeway these days :).

But I did begin with the three $99 RT coupons AmEx sent to student accounts, and I'm still here with DL and recently plopped down $750+ each for a few short East Coasts RTs on short notice-- FWIW in terms of "loyalty."