Regarding changes once upgraded, although your original fare rule change fees are supposed to apply in practice you can standby for the flight once confirmed in business.

However, if you do standby you may get on the flight, but you will be last on the list for J after all those confirmed on the flight already looking to upgrade. So if siting in the front is important pay the $75 to be confirmed on the flight and then waitlist or confirm.

When J was wide open I play chicken while they upgraded about 15 people at the gate before confirming my standby. But in this case I was also willing to travel on my original flight. The concierge was next to me the whole time so was aware of the game I was playing. When it worked she told me how smart I was to avoid the fee.