Another rookie question, but I have a part (piece of wood, 14' long). If I want to use this part in a different place, and trim the length to a specific boundary, can I do this in the assy, or do I need to create a new part for the dimensions I need? I don't want it to also change all the other 'parts' I have previously placed.
Thanks.
Use an Assembly Cut. There will be a box at the bottom of the feature's property manager to propagate the feature to the Part (see How can I get an Assembly cut or Hole Wizard feature to show in my Part file? for a screenshot). Make sure it isn't checked. Also, in the same section of the property manager, there are boxes for which components to have the feature affect. Choose "selected components" first. "Auto-select" will likely be selected by default. De-select it, then select which component or components you want to cut.