I'm not an engineer but my instinct says they could not be reindexed -- at least not without a huge cash outlay and access to a facility with engineering talent and capable of heavy forging and fabrication.
The bars were made, pre-stressed, heat treated and the works thrown at them to give a specific amount of lift at a given weight and not break or lose strength when at maximum twist. The original 55 issue bars were found to be less than satisfactory on some heavily optioned cars so a limited quantity of new bars were made with an additional twist to provide more lift.
The arms are heavy forgings. IMO, that would be the only logical place to do any index changes. Whether you could find a place to make something and afford to get it made and treated would be the question. Broaching the hex shaped hole would be an obstacle so cutting and welding would probably be the only hope of modifying an existing arm. I know I would be reluctant to trust a cut and re-welded arm at full load.
The rear stirrups are a welded piece. If any extra lowering were to be accomplished other than shortening the front links, possibly an extra bit could be welded in the middle of the stirrups. That would allow for a bit of a drop but no idea how much would be possible to add without causing suspension issues or for them to become too low and turn into a road obstacle catching device.
One other obstacle to lowering via the suspension is the A arms would be off center with respect to the bumpers as would the rear components to their bumpers. The least little bump would probably have one end or the other smashing into the bumper and then the frame when the rubber is toast.
If you haven't already looked it over, there is an SAE publication on site detailing the design and theory behind the making and working of the system.
https://www.packardinfo.com/xoops/html/downloads/SAE_Torsion.pdfThis Post was from: https://packardinfo.com/xoops/html/modules/newbb/viewtopic.php?post_id=136720