If I'm understanding your descriptions correctly, yes the whole diff gets disassembled. The pinion bearing is pressed off/on and then all the clearances get re set. Aka it's a rebuild of the diff. Plus if any respectable driveline shop was to take on a bad pinion bearing, they would require all bearings to be changed as no tolerance specs exist for mixed/matched new and used parts. Again, aka full rebuild, if you are really sure it's the pinion bearing.

88 Montero, StarQuest turbo, Kormex 5speed +tuff-pan w/phoenix f. stage2 clutch, 4in lift+33' tires, 4.875 lsd, short-throw shifter, Aisin hubs, SR big brakes, gen2 uca's, elantra alt, and so much more... 16g turbo w/hardpipes + 4.90 locking disk-brake axle soon (maybe lsd or aussie front??)