Shorten sleeves on a denim shirt with buttons and buttonholes is another one of those alterations most people shy away from. How many times do you come across a shirt with buttons and buttonholes and it needs to be shortened? Well this client did not want to pay me to shorten at the top of the sleeve. He said just cut and sew. I couldn't just cut and sew. But to explain about why would have taken a while, so I took the job, and though - "I will do a video of it".
The best solution would be shortening from the top of the sleeve. But if you ever come across something like this and want to shorten from the bottom here is how you would do that.