My understanding is that there are additional rules that apply to all fares, unless contravened by something in the specific fare rules used to ticket.

Be aware that when a ticket is changed, there seems to be some sort of notification to the plating airline. I purchased an ex-SEZ ticket and about a month later, since the fare was still there, had my TA change the dates and the route of the last flight. It auto-priced and I had new e-tickets right away. But the next day BA notified the agency that the ticket was invalid and ordered them to cancel it and refund it, withholding the 5% cancellation fee and the $125 change fee. My TA created a new itinerary and ticketed it, and I of course have not changed it. But the act of changing the first ticket, even though it auto-priced, caused it to come to BA's attention. I'm upset at being charged the 5% cancellation fee when BA was the one who ordered it cancelled, and the $125 change fee as well. But I am afraid of doing a charge-back with the credit card company because I don't want BA investigating and then cancelling the new ticket.