Is it necessary to replace the crown wheel bolts on 8-3/4 ?

Better safe than sorry.
The factory isn't in the business of selling bolts, they are more about protecting their warranty and their image.
The bolts themselves do take a lot of stress when the car is abused.
When the rear diff's crown gear was installed, i bet they used loctite thread locker on the threads and that stuff is hard to get off completely especially on fine thread bolts.
If you don't get it all off, the torque reading would be off on re-assembly.
Time is money at a dealership.
So, unless you idle around town and never drive the car with sticky tires and abuse it .......EVER.........i would just change them out. Same thing if you don't know the rear diff's history or how it was treated.
It's cheap insurance.............