Yes it will reduce the risk.
You think if someone is intent on assaulting a woman, a sign on the door will stop them?
No I don't think a sign alone will stop them, that would be stupid. But going back to single sex spaces and being allowed to shout it from the rooftops if a man enters them will help.
You think these guys are opportunistic and only commit the assault because the woman is right there in the changing village with them?
I think these guys are opportunistic yes, but that's about all I agree with in that sentence. Opportunistic predators are... well opportunistic, so they will use any opening they can to their advantage.
For the last few years women who spoke up (or wanted to) had the additional fear of speaking out to worry about on top of predatory men, because of no debate, the "twaw" bullshit lie, no platforming, police over reach, loss of employment, services and health care etc etc etc.
Now that we are slowly moving back to normality and the law has been clarified by the SC who have stated that sex always meant biological sex, women can now feel confident that if a man enters a single sex space, they can speak out, they are right to do so, and their rights to this single sex space are backed by the full weight of the law. We are returning to a time where we can say the "good men stay out so the bad men stand out".
I don't think sexual violence perpetrated by men will ever be stamped out unfortunately, but swinging the metaphorical doors wide open and saying "all comers welcome" was not exactly a clever plan to reduce risk or harm was it? I mean why put up any barrier to any crime right? Criminals are going to do whatever anyway so why not just let them? That's basically what you are saying, and it would be lunacy for the world to run that way.
We have laws and other social barriers for very good reasons, removing them was obviously going to cause those with criminal or predatory intent to celebrate the idiocy, and it obviously was going to (and subsequently did) cause incredible harms to women and girls that otherwise wouldn't have been put at such risk.
So what is it, do you think that removing all lawful and social barriers to single sex spaces is going to help somehow? If so how?
How would you "stop" these predators if you don't think laws or social barriers will help reduce risk?