Why would you not want Bevel Alpha to move with the object when rotated?
OK, I thought about it, so I’m thinking maybe you want the light source to appear to stay in the same place as the object rotates?
This expression on Bevel Alpha’s “Light Angle” seems to do the trick:
value – rotation
This will allow the light source to stay put as you rotate the object, regardless of where the light source starts, or to be wherever you animate it too, that’s the “value” part. The expression just subtracts the layers rotation from the value (constant or animated) of the Light Angle. If you are going to animate the Light Angle after the expression has been applied, it’s probably easier to shut the expression off (click the equal sign next to the expression) then set keyframes, then click the equal sign again, turning it back on.
Is this what you want?