Take it down to nothing but the shaft, put bottom part in vise, attach a slide hammer to the top nut and pull on it till it’s the right length. Only simple option.
In theory I could do the first bit without disassembling further because I have access to the top threaded portion and also the bottom of the shaft. Not sure if I might damage anything if I did that, in theory I shouldn't as far as I can think about it. Again, if necessary I'd disassemble but just thinking about it. Then comes the main question, whether to 'set' the length or not. That may be answered by how much force it takes to move the shaft and how tight it is after that..........
If your planning on pulling it apart with the steering wheel hold down nut, you need to pull the shaft out of the column. The top bearing is held in the column by a screwed in plate and has a spring clip on the top side. Those things set the height of the steering wheel on the outer column. If you don't want tp take the column apart, you need to pull the shaft to extend it at the shear pins from the bottom of the column.
The force required to pull the two shafts apart isn't very high, once the pins have been sheared, but the fit isn't loose, it won't fall out by holding it vertically, you will have to pull it apart. A good thump on the bottom end will shorten the shaft though. The more often it gets pulled and pushed, the easier it moves.
I would not be concerned about locking the shafts into a specific position after they have been moved. There is not enough space in the vehicle for the shafts to come apart without major body damage. Once in place, the lower connection on the steering box is designed to float in and out, the odds of the inner and outer shafts moving isn't very high unless there is compression in a crash.
