Samsung can do anything they want. If you think whatever that is violates a law or your rights as a consumer its up to you and/or whatever governmental agency is involved to get them to do something different. That could take months. Many months. In the meantime you'll be stuck living with whatever decision they make - whether it's "legal" or not. Fighting multi-billion dollar conglomerates isn't for the feint of heart.
Sadly there are people who've tried to do the right thing that are stuck in Samsung's matrix and no law or governmental agency has rescued them. I can't imagine said agency's will feel a lot of sympathy for people who've held on to a phone declared potentially dangerous by its manufacturer for the length of time being discussed here. "I kept my potentially dangerous phone because I didn't like any of the alternatives" or "I was waiting for the Galaxy S8 to come out" seem like pretty self-serving reasons not to take advantage of all the remedies (including a full refund) Samsung provided. This isn't black and white and certainly not a typical "fit for purpose" issue.
All doesnt matter and all goes against the law, just risk of hazard makes them liable indefinitely until its back at their possession and no harm caused during the time.
Im no fain hearted and I dont own 7 figure bank account but I know its not a rocket science to bring giant companies such as apple or samsung to their knees, again, its not for faint hearted, I was talking from a legal stand point.
Darkness and high-cliff edge walking heights are usually appearing dangerous things for most, until they're certain and know there is nothing dangerous/hazardous in the dark and walking the cliff edge not without protections and precautions, metaphorically speaking.
Take a case where mobile phone gets on fire and one or many people suffers fatal consequences, days, months or even years from now, and investigators dig up samsung note7, who they gonna blame? Who has the case against who? Looking from even early state all cards are against samsung where there disaster happens or not samsung should be waist deep to do whatever necessary to sort their clients out. And yes they can try to attempt "write their own laws" warning consumers, threatening with return closing deadlines, refusing to take back dangerous devices back in, blocking devices, etc its their cards their game against everyone, not that they are more than the majority, I call it one against all and no matter how much money they are worth, it can take just few big cases and they will soon realize what wrong turn things can take, not that they would be willing to take such risks when and if case is brought to the round table.
Heck, even a 3 year ago my 10+ year Honda got a safety recall letter warning about potentially defective airbag systems and all was replaced at surprisingly my convenience cost free, even the car was bought second hand and I am probably 3rd or 4th owner of that vehicle, auto manufacturers know about how this game be played out i suppose, has been in this game before or seen it happen, consequences are clear to them if potential event take place, they would not only put someone deep in dirt, they would be there themselves as a consequence, so they took no risks, and I was pleasantly surprised at the same too how much forthcoming they were to sort this out, and note - this is 10+ year old product, not much different case to the one were talking about here, and I believe if they went this far with thing such as this, how much further they would have taken things if they would have found out that these vehicle models would have been a hazardous risk of fire and explosion while driving, parked at house garage etc? Go beat this statement