He’s asking about jacking up the back end with the tranny in Park.
Yes, it should be in park. It does not put added load on the pawl, because lifting the rear on jacks doesn’t change the angle that gravity is acting on the vehicle, like being on a hill does. The load on the wheels is still straight down, and the load on the parking pawl is as it would be had the rear end not been jacked up.
Bottom line: if the position of the car would not make it roll, it places no added load on the parking pawl. And jacking up the rear end would not make it roll.
As regards the parking brake, it’s pretty hard to work on the rear brakes or rotate the wheels with the parking brake on. 