If it's for your own campaign, then just taking classes out sounds pretty easy. And you may not have to do even that.
In terms of Wild West/Wuxia power groups, you've got:
The Natives: (Aboriginals, hermits, wild men, etc)
Barbarian: Native American warrior class
Druid: The Native healers you go to when you can't go to the town doctor
Ranger: Skilled woodsmen with some knowledge of the Native ways
The Locals: (Common folk trying to make it in a rough land)
Bard: Minstrel, jack-of-all-trades class -- Maverick in a Wuxia western
Sorcerer: Untrained but naturally skilled
Fighter: A gunslinger or a hired sword
Rogue: Another jack-of-all-trades who has no magic but better swordsmanship
The Government: (Representatives of a distant but mighty civilized world)
Paladin: Swordmasters and destroyers of the unclean
Cleric: Spreading the faith with powerful magic
Monk: Agents of the government who need no weapons to do their jobs
Wizard: The learned scholars who hold the true arcane power
If you set up class distinctions like that, then you've got most of what you need. A lot of magic is changed with flavor. (Personally, in wuxia, I'd change cleric and druid to spontaneous casting classes and ditch wizard altogether.) After that, it's just individual rule changes -- like how far a given Jump check lets you go or what the Balance DC is to run along a wall. Ideally, you drop the DCs a bunch, or multiply all results by 4, or something like that, to get the feel you want. (And you may have a rules supplement that already does this -- I know someone was advertising "setting change"-type quick rules that would do this kind of thing.)
So yeah, I could see that working pretty easily. The key for me would be restricting spells on a case-by-case basis, making sure that everybody was on-board with the flavor, and keeping the levels relatively low. (And possibly, for magic classes, requiring multiclassing to keep things in line -- all wizards must multiclass with monk on a 1/1 basis, for example...)