I don't think anyone knows what the true legal status is. As far as I know the locked gate is still in place which means that yes, you will have to backtrack.
If you do attempt it in winter bear in mind that if there is a lot of snow and/or wind you probably won't make it over. Drifts tend to fill in the slightly sunken parts of the track and block it - see a recent issue of LRW/4x4 magazines. There has also been controversy in recent years about some idiots leaving the track - don't do this. At this time of year you will avoid the busiest tourist season however you are bang smack in the middle of the stalking season (stags) for highland estates, so there is more chance of meeting a landowner or employees.
Hope this helps.
