Ron:
If I understood you correctly, you want to be able to go back and work on other parts of this long clip separate from long clip. I had a similar issue last week with PD 15. What I did was:
1. split my long clip(s) as there were three tracks on the timeline and then highlighted the section I wanted to copy. Let's call this Project 1.
2. After that I highlighted the section I wanted to copy to the clipboard.
3. Next I clicked "File, New Project. After saving Project 1, I pasted the clipboard item from Project 1 into the new project (Project 2)
4. Then I saved Project 2 as a new project file.
I might be off on what you were asking but this worked for me.
TeeMan