It appears that the deadline for week 20 didn't take into account that there is a game played before the deadline. The match between Philadelphia and Colorado has just finished and I am still able to edit my roster. Unfortunately I don't have any subs to bring in any of the goalscorers (Nyassi, Mastroeni, Torres). However, I was able to switch out Williams (who had a yellow and red card in the space of 3 seconds) for another defender who hopefully will score better than the -1 point of Williams.
I am unsure if ESPN will realize this error and try to fix it or not, but it is worth a shot to try to take advantage of.