This is a great update!
I had only seen your story today, had I seen it then, I would have probably made many of the same suggestions. I think the only thing I might have suggested if it had been an older snake and not a hatchling, would be a parasite check or general deworming just in case since they can sometimes be known to cause issues like that. In hatchlings, I think more of the issue I've seen is just that they don't have enough muscle strength to 'contain' the bowel after the initial stressed prolapse and need a little extra TLC to get things to where you are today.
Interestingly enough we had a vet for Petsmart do a purse string suture for a chronically prolapsing hatchling a couple years ago. It's a VERY simple procedure and takes only minutes. It worked great and after a couple weeks of feeding very small meals (just pinky mice) we slowly moved up to the right size and spaced out the feedings to every 10-14 days just to make sure the poop was moving well and not causing issues.
I wouldn't be surprised if that was where Petco was leaning to go with that. A lot of the care depends on where you are and who you have access to. I was really lucky and my store had access to 3 vets in the building who were willing to look up info and TRY when we had emergencies. And we had a local reptile specialist we were approved for, but that was usually the follow up as his waitlist was always long. I've seen other stores where the care can be so frustrating because they can't access that sort of medical team. Those are the stores that seem to have the least knowledge in the employees and then the vets just won't understand. And of course the problem with big box stores is really that they just want to make the money off the merch. They don't make much off the animals themselves and they don't do enough to train people to care for them.
I'm so glad you were able to look past that and that you were able to find some great advice. ♥