Yes the ball joints can be replaced, and I have a brand new set of the premium "forgeline" ones I could sell you if you want (long story, see my thread on the topic if you are interested)
You can replace the entire A-Arm with the ball joints and bushings if you prefer. If you use the standard OEM ones, with the OEM bushings, there should be no issue with the EPAS shudder. I'm pretty sure you can also use the GT500 a-arms, which have slightly firmer bushings, with no EPAS shudder problem but I am not positive. The shudder issue happens if you replace the soft OEM bushings with hard aftermarket poly ones; which means you cannot use the Steeda or BMR a-arms that come with hard poly bushings.
Yeah I'm looking into the GT50 A-arm right now. It looks like they are the same part number as the regular GT? At least for the 2011 year, I'm unsure if any other years for GT500 are different/interchangeable.
2011 GT Premium 401a
UPR Oil Seperator | Borla S-Type Axle-backs | Bilstein Struts/shocks | GT500 Strut mounts | BMR Springs | BMR UCA | BMR LCA's w/ relocation brackets | BMR Panhard bar | MGW Race Spec | Dark Stainless SVE Drifts w/ Nitto 555's | JLT CAI | Lethal Performance 3" Offroad X-pipe | Tuned by Kevin @ Wicked Motorsports | 394whp/389ft lbs SAE | 12.74 @ 114 mph