I have an upcoming UA award as follows:
MCI-ORD-IAD(5-day stopover in DC)-CDG(week in Paris)-ORD-MCI in business class.

We are considering spending the first two nights of the 5 we have on the East Coast in New York. I *think* this means we will have to buy IAD-NYC-IAD tickets since we are using the stopover in Washington. (We have a commitment in Washington that means we have to be there for the final three days of the stopover time.)

I have three questions:
- If I buy a separate ticket on UAL metal (IAD-LGA-IAD) departing, say, 90 minutes after my flight arrives at IAD on my award ticket, can I have my bags checked through automatically and get all BP's at my originating airport?
- If I find cheap shuttle tickets, is it allowable to change an award flight from IAD to DCA without penalty? My award ticket would then be MCI-ORD-DCA-Stopover-IAD-CDG-ORD-MCI. Is that legal? I'd obviously have to collect my bags at DCA before checking in to the AA flight.
- Am I missing any other options here?

(FWIW, IAD-LGA-IAD is about $180 R/T for my dates/times. DCA-LGA-DCA is about $50 cheaper. I have the same status on UA and AA - PremEx/Platinum.)