Anyone knows how to make the "Movement Dara Overrides" that is greyed out in some animal races (while others seems to be enabled) to enable it?

Example, HareRace under the "Move Data" Tab has the "Movement Dara Overrides" enabled, while DeerRace (and many others) have that option greyed out, i want to know if there is a trick to enable that option... i ask because i want to stop animals from moving extremely fast while in "Swimming" movement, so far i fixed the Hare by adding a new Movement Type with slow movement, but like i said other animals just have that option greyed out... there got to be a way to enable it and if anyone has any ideas let me know.