You don't need the CS Extender for this, nope. Search and replace is a function in the vanilla CS, found at the bottom of the dropdown list that appears when you select "Edit". Select the item you want to replace by clicking it in the render window, then select "Edit -> Search and Replace". A box will pop up containing the name of the item you selected, and there's a window below that which you can use to select any other item in the CS. You can choose to replace just that one item you selected, all items of that type in the current cell, or all items of that type in the gameworld.