The last time I flew in on UA I was on the left exit on your drawing and don't think there was a way to cross back but I could have been mistaken especially as I try and avoid MCO now. Or if one takes the exit for A or B it may differ.

I do recall once last year a woman did try and get back in the train and a TSO yelled at her and ran over to stop her from doing so.

Same term applies as above.