I had one customer gasp when I twisted the safety chains to shorten them. "You shouldn't do that!" Well, I was a little surprised and asked why not. Apparently someone years ago had admonished them for doing the same thing. This might have come from some trucker or professional tow truck operator who lends credibility to such a lesson. Having twisted chains all my life towing boats and trailers, I just had to do some research.
Luckily, someone classically trained in scientific method and with access to serious testing apparatus had done the research some time ago. The ASME (American Society of Mechanical Engineers) in fact. You can search for it yourself if you want to see the nitty gritty by searching for "Effects of Twist on Chain Strength and Fatigue
Performance: Small Scale Test Results" January 2011. The PDF is freely available.
The bottom line: "The tests measuring the breaking load of the chain between 0° and 24° twist/link showed an insignificant decrease (<5%) in strength compared to the untwisted chain breaking strength. " Furthermore, "in some cases even seeming to indicate an improved fatigue endurance with increased twist"
The breaking load of a typical safety chain typically installed on our teardrop trailers is commonly around 3500 lbs per chain and might be 5000 lbs. Soo, let's say with a medium weight chain, minus the 4% reduction in strength (worst case scenario as far as I can tell), we have chain capable of handling a load of 3360 lbs. Each.
Bottom line, twist your chains to shorten them with the confidence.