They still use the fast pass lines for ride swap - at least that's how it worked for Rise of the Resistance. I haven't tried other rides, but I'm assuming the same.
Just trying to plan our MK morning. We’ll be there before opening but I think swapping will eat up a lot of our time. We were planning to do 7DMT and Space first but we’ll have to swap for both.
And just to warn you, they will only let you have 1 child swap at a time. We had my husband wait in line for Millennium Falcon and I got a child swap, but I didn't ride right away because our boarding group for Rise was called. Later in the day, we tried to get another child swap for Slinky Dog Dash and they wouldn't give us one until we used the Millennium Falcon one or they could delete that and give me Slinky.