My bees don't need any more stores on top of a full National Jumbo.
Some around here over-winter on a single deep; I always left them a super as well. Further north one goes, the more stores they are likely to consume in the cold months(colder and more of them?).
There are things to consider such as whether this 'extra super' is going to be proper honey or sugar syrup and how you are going to make sure, if sugar syrup, that it is not left in the super, next season.
Feeding fondant is another option, if hefting indicates they are low on stores later in the winter or early in the spring. Remember you will want the brood box partly empty for brooding in the spring.
So there are plenty of options and they all depend on lots of possible variables. For instance some strains of bee carry on producing brood long after others have 'shut up shop' for winter. They might starve themselves by January.
As is always the case, observation and being ready to act are the key points with beekeping. Experience with your particular bees/ hives/location will come in time.
BTW, don't forget to remove any queen excluders fitted, for the winter months.
RAB
