Unfortunately, there is no Beam End Angle setting so you would have to resort to workaround and that works only when the end angle is less than 90 degrees. So it does not work in your case where the angle would be 120 degrees.
I would probably convert that Beam element to a Morph and use the Split command to Split the Morph at the desired angle in two pieces. You can then classify the Morph as Beam so it will schedule correctly.
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