When creating Soft Object Variables of Actor or Character blueprints, the default value of the variable is greyed out and unable to be changed. I was able to create a Soft Object Reference of the Third Person Anim BP and the default value was not greyed out.
Tested in //UE4/Release-4.25 @ CL 14469661 and this did not occur, so marking as a Regression
The default value is greyed out and cannot be changed
The default value can be changed in the details panel
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-109717 in the post.