If I understand your drawing, changing the angle will result in a a couple of the surfaces becoming longer. Depending on the source drawing this could be at the start over drawing time. I only have experience in Autocad and Fastcad. I detest Autocad because of the hardware requirements. Still on a Pentium 4 processor. If you doing detailed scale drawings the average mouse is not going to cut it. To modify the drawing it needs to be in one of the native drawing files DWG or DXF so it can be imported; example. Then there is the possible issue with the version of the drawing file and the software. It might be time to see if there is a draftsperson near that can do it for you.
I got out of the drawing business when the software versions started changing twice a year.
If you hire someone make sure you get the drawing in both formats, and that the software and version is listed on the source drawing. They will not want to do this. I hired a draftsman for my house, in the contract I stated both drawings, he furnished pdf and refused to provide the other. After the judge decided in my favor he destroyed/lost all of my originals. Or so the story went. Needless to say he never got his full payment.
I can be no help with anything about 3-D.