Hi
Once you have set the IN/OUT points using the Clip Preview screen and "Placed" the resulting clip section onto the timeline, the IN/OUT points will remain associated with it.
If you now want to use the same clip again just select it again from the clip bin. (You will still see the original IN/OUT points in the clip preview screen but you can now ignore them.)
You now select a new section of the clip by simply moving the IN/OUT points to new positions and then "Place" that on the timeline. Your first selection already on the timeline will remain unaffected.
Obviously if you want to use the whole clip just move the markers to the start and end of the clip and "Place" The down arrow next to "Place" will give you options to where you may want to position your selection..
Nat