Just de-power the rack. It's not that difficult at all to tear the rack apart and cut the valve out of it. It took me like an hour. Although I had the engine out so removing the rack itself was easy.

There's no need to remove the header, and the added work would be far greater than any possible benefit. If the header was already out, or it was coming out anyway, that's different, but I wouldn't remove the header to facilitate removing the rack or any other part of the P/S system.

my .02:
First NA I had was factory manual rack. I've owned a few with PS as well. Did the FM depower on one car. Drove another with looped lines.

My own feeling is that the factory rack was the best. That's just personal preference, I understand that a lot of people don't like the ratio/number of turns. I don't track my car so maybe that is more important there. To me the feel of the factory manual rack was just better than the depowered ones. Maybe because of the difference noted in the miatabusa article.
I have a (crappy) welder, but I understand that the weld mod described must be done very carefully and properly, so I opted to purchase a factory manual rack and swap. Note that there are different part numbers for the inner tie rods, and the washers.

I've heard that the NB's manual rack, which is pretty rare, is much better than the NA's manual, though I did not hear why. The two aren't interchangeable, so far as I know only because of the mounting differences, though there may be others. The NB's mounting method is superior, never felt great about how the NA's mounts up. Purchased superpro rack bushings to try and stiffen up the assembly. FM sells them. Note there are different parts for PS/MS

Manual racks are usually available on ebay for $120 or so, I got mine there for $60 because it was encrusted with rust and crud, but it was nothing that a wire wheel couldn't fix. because you'll need to change the inner tie rods, might as well change the outers too, and maybe the lower ball joints. There are sellers on ebay that sell no name brand combo's of the 3, I think about 70 shipped or so.

I say listen to this guy