The way I read it, it says they get to "freely" change the engagement range, which to me signifies that they get to forgo the whole Evade opposed roll and get to their desired distance.
For example, Shortsword Sam is being held at bay by Longspear Larry. Longspear Larry attacks and succeeds with a Normal Success, but Shortsword Sam parries with a Critical Success and gets a CM. In my book, CMs are rewards, so Shortsword Sam gets to change range and get into close combat with Larry without Larry getting to try to Evade.
I could be wrong. "Freely" might mean they don't have to spend a Combat Action to do it, but I will run it as above unless one of the greater mongooses corrects me.