Pass/fail is no longer linked specifically to 'extra courses'. The policy details are available under the Academic Standard and Regulations link.
You may not designate the pass/fail option during drop/add. The option will be available between the third and tenth week of classes. You really want to wait until you have graded feedback in all your courses before you consider designating one as pass/fail. There is an online form to designate the pass/fail option, due no later than Friday, November 18.
Highlights of the new policy:
You can check course descriptions in the online catalog to see if the pass/fail option will be available for a particular course. Drill down through the catalog links to the full course description. Under the 'Additional Info' or 'Additional Info 2' sections, there will be an indication if the course is not available for the Fifth Course option and/or if the course cannot be taken on a pass/fail basis.
If there is no mention of the pass/fail basis in the 'Additional Information', the course will be available to be designated as pass/fail.