hey Rodger ,i have moved both my front and rear axles by drilling new holes in the spring perch on the axle .
i did this for that exact reason on the rear i did not want to source a shorter driveshaft ,so i moved the axle back to match the length of the driveshaft i had . i too am not sure of physics with the springs , but my understanding is that the spring pins primary job is to hold the spring together and to locate the axle in the proper location , i have noticed no adverse effects from moving the axle on the spring ,
the first time i did an axle relocation i re-drilled the main two leaves and then just relocated the rest of the springs to the new location, i did not re-drill all the individual leaves , one of the main leaves actually cracked through the original hole breaking the leaf in two after a few years so i decided against drilling them the second time , oh ya its hard to drill spring steel also by the way ,lol there for i just replaced the springs and re-drilled new location hole into the axle spring perch itself ,super easy , drill new hole where u want it and you also need to drill new hole in the U-bolt plate too .move axle to new locating hole and bolt her up ,my rear axle has been moved back about an inch on the new hole and i haven't noticed any adverse affects ,been like that for around 20 years or so,the front i did for a different reason , if you go too far forward on the front you will have issues with your steering components hitting or rubbing ,
not sure if that helped , im horrible at expressing my thoughts on a computer hahaha
cheers Jake