How to use local angular velocity?

I recently found some script which suits the game I am trying to develop, I require it for vehicle movement, this script being.

Vector3 localAngularVelocity = transform.InverseTransformDirection(rigidbody.angularVelocity);

It is supposed to get the local angular velocity of a rigidbody, however when I try to change a value of the rigidbodies local, it simply doesn’t work, I’m trying as so:

rigidbody.transform.InverseTransformDirection(rigidbody.angularVelocity).y += floatvalue;

Any suggestions as to how this piece of script would work?

Note: that code using it is to rotate the car around it Y axis so it can turn at varied X and Z angles.

Many thanks in advance, Ben.

Unity Scripting API on Rigidbody.angularVelocity says:

In most cases you should not modify it directly, as this can result in unrealistic behaviour.

Use Rigidbody.AddRelativeTorque(torque, mode) for this.

But, if you still want to change this directly, you have to do it this way (actual for Unity 5.x):

GetComponent<Rigidbody>().angularVelocity += transform.TransformDirection(new Vector3(0, floatvalue, 0);

Though I might be wrong.