The diff pin has to come out to allow the axles to slip in a bit so the retainer clips will come off the axle. Do both seals, since you have to pull the cover off anyway.
The problems you may run into include the 5/16 head bolt that retains the spider gear pin can break at the end of the threads. 99% of the time, if you don't panic, this is solveable with a can of brake cleaner and a small, sharp pick. Spray cleaner liberally around the pin, in the bolt hole, and just use the pick to twirl the remains out- there is almost always a tiny bit of thread left on the portion of the pin broken inside the housing. New bolt available at any GM store.
Second problem is the bearings run directly on the axle shaft, and the hard surface may deteriorate over time. That requires new axle and bearing, which is a pricey fix, because new is $$, and junkyards know it. There used to be an "axle saver" bearing, which moved the rollers outboard to a new chunk of undamaged surface. They don't work great long term, the seals are tiny compared to the originals.
When you put the new seals in, always put a swipe of silicone sealer on the steel shell of the seal, where it goes into the axle tube, or oil will seep out past the two steel surfaces. A good seal may have a rubber coating on the outside, but I don't think you'll find ones like that for this app. I would spend the extra dough for GM seals, or at least inspect the aftermarket ones to be sure it has a heavy duty multiple lip seal surface.