Make a constraint dimension unlocked?

[jboyceQPURR]

So i'm  trying to use the value of the constrained dimension below. I use that 100 degrees or what it is, in a formula for 2 of the other angles. the 50 degrees angles are always half of the 100, so it' s a formula. Ideally thought I want to be able to stretch the lines/shape and have the 100 degree spot come up with the angle on it's own, similar to how a normal dimension works. I can't use a normal dimension though because it doesn't let me name it so I can use it in a forumula. Is there a way to unlock the 100 degrees so it will update when I move the lines?

[jboyceQPURR]

Here's a quick video of me using this. The idea is to have these corners auto update when it moves to any angle. But I want to use a point and stretch in a block, not manually input the angle every time. 

https://drive.google.com/file/d/1K_2mz-SnFaEnE3esdgbl5hIiHloEB8Fa/view