This is standard language for weather waivers. You can change for dates outside the window and still have the change fee waived, you'll just have to pay any fare difference.
"When rescheduled travel occurs beyond January 23, 2019, the change fee will be waived. However, a difference in fare may apply."
Yeah, I've had luck moving to a flight outside of the end of the waiver date if I have a good reason. I've only had to pay the difference in fare a few times... it's never been more than $50. This could depend on a lot of factors, though (including how willing the agent is). I think they can also look at historical fares based on when you booked your ticket. Not really sure.