The track bar length is very easy to set and no, the alignment shop will not adjust it.
To set the track bar length, it's darned near automatic. Disconnect the track bar from where it is mounted to the passenger-side mount on the axle. Stand on the bumper and jounce the front-end... jump up and down on the bumper. That will allow the coil springs to center the Jeep over the top of the axle. Then adjust the length of the track bar so it lines up with the mounting bracket and the bolt hole. Your track bar is now set to the correct length.
Don't pay extra for a 4-way alignment, there is nothing the alignment shop to do for the rear axle.