If the main goal is to reduce injuries, the most effective approach the ISU could take might be to bring back school figures and to require only double jumps in the junior short program.
I don't think that approach will fly.
Regardless of any rule changes, it would be nice if the ISU could compile the best current scientific knowledge from around the globe about optimal training regimes to develop strong capable athletes with reduced risk of injury and disseminate that knowledge to all federations, aim it at all coaches (elite, developmental, and recreational -- probably with most emphasis on developmental coaches.
It would also be nice if they could commission research studies to expand that knowledge base (with what money, though?).
Although I don't expect school figures to be revived or jump content limited significantly especially in free programs, it would be possible for SP requirements to require more skills that demand core strength and precise edge control and general quality of movement, with less emphasis in the scoring on jump rotations and extreme flexibility.
In the free skate, there could be more emphasis on quality in GOEs, of the sort that represents well-trained bodies and not overtraining with both judges and skaters/coaches educated about what is to be most rewarded. There could also be more options for different ways to earn points in the free skate so that skaters who can do quads easily have that option available to them but will not necessarily outscore skaters with lower-rotation jump content. Find other kinds of jump difficulty to reward and build those rewards into the scoring system just as higher rotation is already rewarded. Continue to reward Biellmann and other flexibility positions in spins for those who can achieve those positions easily, but with more emphasis on quality than difficulty, and also add (or allow multiple uses of) features that add difficulty through blade control more than positions, especially extreme flexibility positions.
And perhaps raise the program component factor for women and pairs to match that of the men. The technical base values will still tend to be lower than the men's for most competitors in those disciplines, which means that PCS would be worth more proportionally.
If long careers is a goal, irrespective of injury, then giving more incentive for skaters to stay competitive after high school age, even if they come from countries with deep fields of younger skaters who can temporarily outjump them.
For ladies especially, that might mean a developing junior event, a high-tech-value championship that's designed for ages 15+ but allows in technically exceptional 13- and 14-year-olds, and a well-rounded senior championship with more emphasis on quality and PCS than on jump content.
Or it might mean allowing up to 5 or more entries from the same country at Worlds (and Euros/4Cs?) based on a combination of last year's results and wildcards for specific high-achieving skaters in the current season.