Stroh, while 4-2 applies the guts of what you're looking for are in appendix II.
All clubs may incorporate mechanisms for weight adjustment. Other forms of adjustability may also be permitted upon evaluation by the USGA. The following requirements apply to all permissible methods of adjustment:
(i) the adjustment cannot be readily made;
(ii) all adjustable parts are firmly fixed and there is no reasonable likelihood of them working loose during a round; and
(iii) all configurations of adjustment conform with the Rules.
During a stipulated round, the playing characteristics of a club must not be purposely changed by adjustment or by any other means (see Rule 4-2a)
Arguments abound as to what constitutes "readily made." Seemingly an adjustment made by a screwdriver or a dime is a problem but that made by a hex screw is not.
If you can buy the tool at Winn Dixie you're in trouble but if you have to go to Home Depot you're golden.
re: Golf is still hard.
Over the past decade or so the average USGA handicap index has dropped by 2.x strokes. Anyone who has tried to shave strokes off their index knows that's substantial. This has happened with plenty of courses increasing length, speeding up their greens and/or growing their rough. This has also happened in the Tiger Era when plenty of new players started up with the game. That should be raising the average index although admittedly many of these noobs don't carry a handicap. I look around (and in the mirror) and I don't see this happening due to the fitness revolution sweeping golf. I hit a couple of 300 yard drives today using a R540 350cc driver. I'm short, overweight and my swing isn't worth filming to say the least. I was hitting it pretty good and basically all of my drives were 260+ other than the one I duffed and the one I sliced. Dan Pohl led the PGA Tour in driving distance in 1980 with an average drive of 274.1 yards. I think it's pretty clear equipment has helped the weekend golfer to a pretty significant degree.
For professionals and top amateurs the difference is even more substantial. They are hitting 9i second shots into 500 yard par-5s. The tournament venues are doing all the things mentioned above and other "elite" courses are following suit. Look at what Augusta has done. Planted tons of trees, lengthened the course pretty much yearly, created bowling alley golf on a course that was designed to play wide open and encourage the hero shot attempt. The Masters has been ruined. I suspect the winner on Sunday will enter the back nine within 3-4 strokes of the lead. We'll never see a Norman v. Faldo classic again on that course. Not unless they roll it back.
Classic designs at 6500 yards which refuse to "Tiger proof" themselves are being left by the wayside. We don't get to see them on Sunday afternoons and that's a real shame. How about mods to our local munis? Probably not so much. The equipment revolution does not touch many of us where we play.
For those that do succumb, how much does it cost to purchase, develop and maintain an extra acre of a golf course? Who pays for it?
Anyway, you've seen the adverts, right? More length, less spin the driver, more spin on the irons, more control, better feel, better touch, bigger sweet spots, optimum launch conditions for everyone who buys one - did I miss anything?
The alternative view? Equipment is not ruining golf ergo the equipment companies are full of *feces* ergo there is no advantage to buying their gear. I'm fine with giving this one a shot too.
Most of the best golf courses in this country at least were built in the first few decades of the last century. A renaissance has occurred in the past couple of decades. In between we have, for the most part, a bunch of cookie cutter, penal, strategically wanting designs culminating in everything all things Fazio. I guess people like that stuff. I don't.