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..........
