I'll share my experience on this:
I'm changing dampers on my A2 so I must separate the lower ball joint from the hub . I didn't have the VAG ball joint press tool that the service manual asks for.
First, to get the nut off I had to heat it using a propane torch (1925 C). I did several cycles of heating the nut for 10-15 sec. Sprayed penetrant on it. Repeat. (I took care to aim the flame up so I didn't wreck the ball joint rubber, and I used a heat shield so I didn't burn the CV boot.)
I had the car on jack stands, so I put a jack under the lower arm to exert pressure on the ball joint so I couldn't spin. That meant I didn't have to faff with a T40 torx to counterhold the stud. Using a 18 mm round spanner, extended with a big spanner to get leverage, I had give it what I got before the nut would release.
To release the ball joint from the hub I used two hammers to bang on the SIDE of the ball joint fixation point in the hub. Perpendicular to the direction of the ball joint bolt. One hammer as counter-hold, one to whack the opposite side. No use of pullers was needed.