On an upcoming trip from MUC-ORD-SFO, I will have to collect my two checked bags in ORD after immigration. I have a six hour layover in ORD.

I am bringing a bag for my friend in Chicago, who will come pick it up at ORD.

Questions:
A. Is it possible to re-check only one bag to SFO? Will United care?
B. If not, may he bring an empty bag to swap out (incl. bag tags from his bag)?

Thanks.