I used ARP studs in my '85 Supra turbo build. I don't remember them ever saying to re-torque the studs but that was 8 years ago. You have to remember that studs have significantly more holding power then bolts and therefore don't require as much torque. But I would certainly check to see if they have loosened at all. You might be able to get away with a re-torque.
'02 Yellow ZX3
'85 Supra 6M-GTE