I would suggest renaming your thread title because people don't really think of "double roundtrip"
Not sure how to, let me know how to and I will.
Going twice to the same destination on the same ticket is not allowed.
In my personal experience this has not been an issue, I know double roundtrips aren't allowed, but this is a multi city BOS-NRT-BOS-NRT-ORD, hence not a double roundtrip. I was able to book RNO-SIN-LAX-SIN-RNO with UA res and didn't have any issues.