Jacking up the hub if kingpin bolt removed could be dangerous and unseat the upper end of main spring as its put into greater compression. There is (or should be) plenty of residual compression in main spring, with suspension unloaded, to hold its upper end in position. If it has moved though, with the precaution of having some temporary but loose locating device in kingpin threaded hole such as short screwdriver or allen key, it can usually be moved a little to realign for ease of kingpin bolt replacement.
