US Airways Dividend Miles (Pre-FlightFund Merger) - Once I check in online, can I still change flights?

I have a DCA-CLT-SRQ 40,000 miles preferred coach award flight tomorrow. I want to avoid any situation that resembles yesterday at PHL. If I check in online for my flights, then arrive at DCA tomorrow and see that one of my flights is severely delayed or cancelled, can I still call the CP line and change to a flight the next day? I don't know if they would have a problem switching me if I had already checked in (though my flights are both zeroed out so they should be happy if I switch days).

Thanks.

You can still make itinerary changes even after check in either at the ATO or via phone with res. Once in a while res will sound confused on the phone about how to change a PNR with an e-ticket showing a CKIN status, but I have never had a situation where they have not been able to do it. Also as long as you have a same date boarding pass you generally should be able to enter security and bypass the ticket counter area.

The only thing to be mindful of is let's say you have checked in for:
Sun Dec 26: 7AM DCA-LGA
Sun Dec 26: 7PM LGA-DCA
Now imagine you call and change your 7AM to the 11AM flight out of DCA. Of course you would need a new boarding pass (obtainable at the gate) for the 11AM flight, but more likely than not, you now would not be checked in for your 7PM return flight if res reissued your ticket. You can often tell if they do a reissue by looking at the Virtually There itinerary, and if reissued, you will see two ticket numbers under your receipt. These days res often does a complete reissue generating a new ticket number even if a change does not incur any additional fee or charge.

Conversely if they "revalidate" rather than reissue then I don't think you would lose your check in status on the return flight.

Of course when they do a reissue they 99.9% of the time don't tell you that the reissue will negate your check in on return flight that you are already checked in for online.

I don't think your doing a same day return, but figured I would post this supplimental info anyway.