Replacing perspectives

In addition to opening new perspectives you can also replace the current perspective with a new perspective. This effectively alters the layout of the current perspective. Editors that were open continue to remain open in the new perspective.  To replace the current perspective hold down Ctrl or Shift-Alt (depending on your platform) while selecting the perspective to open from the Open Perspective button or the Perspective > Open menu. 

When the current perspective is replaced with a new perspective the shortcut bar updates to show the current perspective's button.

Preference options (Window > Preferences > Workbench) allow you to specify whether you want to replace a perspective by default or open a new perspective in the same window or its own window.