Opinions on how to update gs1 upc

I have an asin with an old upc that is non gs1. I’ve reached out to 2 consultants today and I am confused on who to choose.

Consultant A says we will create a duplicate asin with the new upc and then reach out to seller support and have them merge the 2. He mentioned that sometimes this does not take and they have to do it again. He was very confident this was a non issue and was something he routinely did with almost 100% success. He also told me that the process that consultant B suggested would work but that it was slow and not efficient.Consultant A says they can solve the problem within 5 days or so.

Consultant B claims they will open a ticket with brand registry support and once they respond they will escalate ( they would not tell me to who as I think they thought I was just digging for info on how to do it myself) and eventually this escalation will allow them to get to someone who could update the upc. Consultant B claims to have worked for amazon and told me that consultant A’s plan was against amazon policy and not even possible as in order to merge the 2 asins all of the info including the upc code would have to be exactly the same. Consultant B mentioned this would take 6 weeks while they initially said 2 weeks.

I’m at a loss on what to choose here. Is there anyone who has had long term success after updating a upc code? Anyone with real world experience with this?