The arms fit with high repeatable precision thus geometry will stay the same. However, clearly you will still have to adjust VTF, VTA and azimuth for the other cartridge.
Additional armwand for Graham Phantom?
I have a Phantom II and have considered a second armwand for a mono cartridge, but was concerned removing and re-installing the armwand would throw off the meticulous cartridge alignment I did with a Mint LP Best Tractor. It took me hours to get it right. I know I could test this myself by removing and re-installing my armwand, and then check the alignment with the custom made Tractor. But I'm wondering what other Phantom owners think about this. Does an armwand go on and off precisely enough that there would be no change in geometry?