public Keyframe[] keys { get; set; }

This lets you clear, add or remove any keys from the array. If keys are not sorted by time, they will be automatically sorted on assignment.

Note that the array is "by value", i.e. getting keys returns a copy of all keys and setting keys copies them into the curve.

Additional Resources: Keyframe struct, AnimationCurve.AddKey, AnimationCurve.RemoveKey functions.