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Loosen the bolt on top of the lower ball joint about 1/3".
Prop up the rotor/parking brake by a jack (so you can use the spring to help pull down in the next step)
Then put the end of a 12" long 2x4 on the front flat spot on top of the lower A arm and take some good swings with a 3lb hammer. The 2x4 won't damage the aluminum A arm. Eventually the arm will break loose and you can finish taking off the bolt.
...and yeah, don't use those pickle fork things to pry it apart. You'll likely damage the grease joint.
There is a special tool made to do this as well, but for $150ish you don't need it.
So how do you keep the ball joint stud from turning? There's no way to get a torx bit or allen wrench in from the top, the hub is dead nuts in the way.
You can disconnect the tie rod and get a bit more clearance since the hub will turn left/right at that point.
I didn't recall issues with the bolt spinning until I broke it loose, at which point I used some thin soft grip pliers to hold it. You could also cut down an allen wrench to get in there.
Take a look at this link for front bearing hub removal. I recommend that you remove the knuckle completely out of the way. Just remember what ever you do, DO NOT use the pickle fork ball joint separator.
I am just finishing a spindle duct and shock install and can tell you that with the knuckle out of the way things are very easy.
I took an easier (albeit more expensive) route. Since I still had my car on jack stands for the KONI shock and LG/DRM brake duct install I just raised ithe car a little higher and used a ball joint tool from NAPA to remove the lower b-j directly from the control arm.