@starfish2020 - could the pool provide a small, movable screen in the Ladies changing room, that you could use to make a semi-private area for your son to change in?
If they can't do that then I would go down the route of swimming trunks as his underwear on swimming lesson days, so you can just whip his clothes off poolside, and afterwards, when you don't have the time pressure, you can get him dressed in the accessible changing facilities.
In the nicest possible way, I do think you need to take a look at how you have come across on this thread and to see how it might put people's backs up. As others have said, the women in the changing room are not prancing around naked - they are just doing what they are perfectly entitled to do - stripping off to get into or out of their swimming gear. Calling it prancing (or prouncing) was unnecessarily aggressive. And saying anyone who has a problem can use the private cubicles in the way that you said it, did sound pretty entitled, I'm afraid.
I get that you are always feeling like you have to fight everyone, just to get your son the help that he needs, but not everyone is against you. If you had started a thread saying "My son has special needs, so I need to help him change before and after swimming, but there is only one accessible changing facility at the pool, and it's often in use in the short time slot I have, to get him ready. I've been taking him into the Ladies - he's under the cut-off age for our pool, so he's allowed in there, but he looks older, and some people have complained. We can't use the private cubicles, because they are too small - can anyone suggest any ways we can get round this - he needs to go swimming as his physio has recommended it, but we don't want to piss people off" - you might have got a better response.