To clarify, the way your wheels are mounted to the drum assembly is:

Five 3/4 fine thread studs are pressed into the hub and drum assembly.

Inner wheel goes over these, inner nuts (with square end) thread on and are tightened to hold inner wheel on.

Outer wheel goes on over the outside threaded part of the inner nuts, it is held on with the outer nut, a hex nut.

Longer inner nuts (sometimes called thimbles) are available, but they will not move the wheels out, they will just fit over longer studs and have longer thread.

Usually, to replace a stud on the rear, you will have to remove the axle shaft (bolted to the hub with hex head cap screws), then remove the hub and drum assembly by removing the bearing retaining nuts.