If I were simply cleaning and greasing the steering head bearings, I would proceed as you describe. I would block up the fork to limit the downward travel of the fork and then clean the bearings and re-apply grease. There is a compelling argument to be made that it is necessary to hold the bearings in your hand to properly clean and re-pack them. It might be necessary to remove the fork to inspect the race for the lower bearing, but I am unable to visualize the need to loosen the pinch bolts in either case.
It's your bike, and you can proceed as you see fit.

As I discovered last night, there is no need to loosen the pinch bolts. After the top clamp was removed, the whole assembly dropped. That's not to say that there isn't a good reason to loosen them; only that I can't understand why one would need to. I imagined myself lying in a ditch, waiting for the paramedics to arrive, while cursing myself for not loosening them as Snowbum instructed. My bike is a SWB model and after all of the nightmarish stuff I have read on the subject of wobbles, it just seemed to me that the fewer things I loosened the better chance I would have of maintaining what always seemed like a good working alignment. Alas, it is moot because I discovered that my lower race is notched and so now I have to disassemble everything anyway.

I've done this twice, once each to a /6 and a /7. Both times I did as you did, and simply removed the front wheel and fork crown. The forks dropped ~8 inches exposing the bearings. It helps if you have compressed air when cleaning the captive lower bearings in place. Use some thinner to wipe the old grease off the races left in the frame.

Most greases, as odd as it sounds, are not water resistant. Be sure and use a good waterproof grease, like boat trailer wheel bearing grease.

Tightening the head post bearings is the tricky part. You want zero play up-down or front-rear, but still loose enough for the forks to move without any binding.

If your head post bearings need re-packing, then don't forget the wheel bearings.

" You want zero play up-down or front-rear, but still loose enough for the forks to move without any binding."
I guess I am showing my age here, Butt, this exactly the way we were taught to set front wheel bearings on older rear wheel drive cars like a '64 Chevy Bel Air for example.

That's exactly it ! But instead of getting close and having to insert a cotter pin, you can get right on the money. You'll actually end up with a slight pre-load on the bearings. BMW may even give a torque spec.