The precise process to freeze a mesh as hit by a freezegun - asked by OP 2 years ago, is called a Pose Snapshot.
It’s been explained many times, and there is a somewhat comprehensive live training for it that also covers all sorts of other ragdoll issues:https://youtube.com/watch?v=nkj6PAbGYtM
@thelazylion
Not sure if this is what you were trying to do, but you can activate a profile on “all joints below”.
That means that you create a PHAT profile as rigid or loose as you need, and apply it to the joint you want to isolate and simulate on.
-picture it like this, if the freeze gun hits the arm, you freeze the arm in place while the rest still works.