The kicker is, health insurance companies will use any pre-existing condition to get out of paying for just about everything. So, for example, if I wound up getting poly-cystic kidney disease, my insurance company would use the fact that I donated a kidney as a pre-existing condition to get out of paying for it. Even though it's completely unrelated and can't cause PKD. It's an out in their mind and they're going to take it.
Health insurance and medical care in the US is absurdly corrupt. That's why I wasn't allowed to leave the hospital without buying a walking boot from their provider. And their provider billed my insurance company $700. And the insurance company paid them $400. And then the provider billed me $100 and threatened to send me to collections if I didn't pay them. All for a walking boot that didn't fit, that I didn't use, and that I could have purchased from Amazon.com for $53 with free shipping.
Only if they are below the maximum premium profit-to-cost ratio (20/80), otherwise, they are going to have to refund the excess anyway, due to other provisions of the ACA.