In the second case, you're using standby to change a C-D-C RT into a D-C-D RT (i'm using different letters because I'm confused which is A and which A at this point), although you don't have a RT but rather two one way tickets. With separate tickets and separate PNRs, you're not using flight coupons out of order. Also, since it isn't a RT, you're not doing this to avoid a higher fare for D-C-D than the price for C-D-C. Moreover, AA has no way to know where you are--or where you had planned to be--at the beginning of the trip.

It's creative, but I don't see a problem, other than the risk that you cannot get onto the early flight you want as a standby, therefore requiring you to cancel the entire trip (both tickets, so two $200 change fees).