Yes, you will be charged again if you change again.

For the SDC bit you have a decent chance. If you're booked on the early JAX-EWR you can fly on any of the other flights the day prior. You will have the option so long as there are seats open and you are within 12 hours of the NEW departure time. Check out the FAQ sticky; I just added a post at the end about SDC. You would be trying to apply example #1 from that post. You would be hit with the $50 SDC fee, but that is better than the $150 change fee.