My experience showed that you can retain mass with S&S with heavier bells (32kg-48kg), but I was training 5-6 times a week. I had 17.5" arms before and after 6 months of S&S. I did see growth in my shoulders and lats as well.
It’s my opinion that most of us are still fooled by the fitness industry. The industry markets with a lot of articles and ads that feature chemically enhanced subjects to sell you supplements & protein powder. If you take an honest look at all the “natural” strength athletes, there’s not a huge difference in how much mass they accumulated (regardless of what strength implement they use). Even the true “natural” body builders, if you catch them out on the street on a rest day, they’re not that much bigger than other natural athletes or strength competitors that maintain a lower body fat percentage.
If you’re going to do S&S, you are better off just sticking with it until you meet simple standard. When you start adding in this or that, you just impede progress for your get-ups and swings. If you’re worried about losing mass, then crank up your practice by going 5 or 6 days a week and get to Simple faster. Then you can decide to keep going heavier or switch programs. If you can't wait, just jump ship now because there's no use watering down any kind of program.
Also, I quit buying into the whole protein propaganda that the industry pushes. Not saying that protein isn't important, but you don't need as much as what the industry leads you to believe. You would be better off learning how to manipulate the natural anabolic hormone in your body known as insulin to get the amount and type of mass you want through certain foods and diet timing.
JMO, Good Luck!