No it absolutely doesn't have to be "cast in stone for all time" that's absurd. I made the same argument in making a case for the ref pre 2016 that only people who were of majoirty in 1975 could have voted then and that they were a smaller and smaller portion of the electorate as time marched on.
People are perfectly at liberty to campaign for the outcomes they want to see, so long as they do so lawfully.
The question was clear as day
The outcomes were clear. What people mean here is that they wanted a particula r "Leave" outcome to be set against the then present and very general "Remain" position, thereby vastly inflating the chances that Remain would win. Honestly, I thought Remain would win anyway.
Where the "second referendum" crowd would have had my support is if they had accepted the outcome that leave won and then had ref 2. Ref 2 with the options being leave with an arrangement agreed between the UK and the EU or leave without any arrangement in place would have been a totally legit ask. They didn't ask for that, they wanted a do-over and if you're any sort of democrat that's wrong.
In a democracy it is rather important though that the side that wins enacts what they promised to and the side that loses accepts the result. The para above shows the Remain side didn't do that, and seemingly some of them still don't. Anyhow, all old hat now,