A clip can be trimmed in the (video) bin using the Set Start/Set End buttons... 
Then pressing ADD will drop it onto the sequence. Click the caret at the right of that button for more options. Or simply drag the clip.
If changes are made to either the bin or the sequence clip, they will affect that area only. It's the same clip, but changes are independent.
Numerous copies of a master bin clip (usually untrimmed) can be made by right-clicking the clip, choosing COPY, then right-clicking in an open area of the bin and clicking PASTE (insert). Copies will be incrementally numbered and changes made to one won't affect the others.
There's no auto-update on the sequence for clips that are changed in the bin. But an newly edited bin clip can replace its sequence clip as instructed above.