Try like i said with the nut on the opposite end, spray backside of stuch wheel.
When it sticks back through use some emery cloth to clean and smooth it.
After tapping the axle end flush with the wheel hub, I left it alone for a while (I've got dozens of projects in rotation).
I ordered a 3/4" brass drift punch from fleabay and the day it arrived (sometime last week), I put the kart on the floor, stood behind the wheel to brace it and tapped the axle all the way through with nary an issue. So it did sit upright for a long time soaked with Liquid Wrench which definitely helped.
Am I merely going to install my new 6" hex-bore wheels without addressing the rust problem? NO. I am going to grind that rust down to shiny bare metal and either lay down a thin film of anti-seize or paint it first, then add anti-seize.
I will wire-brush the threads too and tidy them up.