"I think Mike is looking for the "auto update" function"
Ideally yes. In Fcp 7 all you needed to do was drag a sequence into a video track. And it would act as a clip, but then you can double click and just load up that Timeline make changes and then go back to you other sequence.
What you can do is making a subsequence of the sequence A and edit into sequence B. Make an IN and OUT and then drag the little sequence icon from your record monitor (the right windows) into your bin and you will have a subsequence. Hope that helps.