When you replace shots on the timeline, you decide whether the edit sequence changes duration if the shot being replaced is of a different duration than the shot replacing it. If the clip you are replacing contains soft effects, you can choose to keep the soft effects with the new clip.

From the EditDesk, you replace shots gesturally in Storyboard view, with hotkeys in either Record Timeline or Storyboard view, or with options in the Src/Rec Player.

From a BFX level, you replace shots using hotkeys.