RE: Retrofitting Longer limb bolts
I once saw a PSE compound bow that a local machinist/bowhunter did extend the limb bolts for the purpose of relaxing the bow's limbs.
He machined the limb bolts out of high-grade steel. They were machined all-thread bolts and were slightly tapered at the outboard end, unthreaded, and shaped so that he could tighten the bolts with a small wrench. The bolts did (obviously) protrude but he had rubber sleeves over the exposed ends.
Keep in mind though; the limbs were longer (longer ATA) on his bow than most bows of today, and the string was attached to "teardrops." He said the system worked well. I cannot say it actually did or if he ever had tuning or breakage problems.