[merlinj79]

I know the recommendation is to have the car level. But I have no desire to be under a car that is up on four jack stands.

I do it all the time, have been for decades. Quality jackstands and I know my driveway is solid concrete (as opposed to say asphalt or hard dirt, where gophers might tunnel). I check the stands carefully and wiggle the car pretty good before getting under though.

Even if the car is nose up, if I get 2L of fluid out, and put 2L of fluid in, what does it matter if the car isn’t level?

You don't know for sure that it was full to begin with, even a tiny leak could add up over many years. I like CalgaryTSX's idea though... overfill and then level it to allow excess to drain out. Then jack up again to install plug.