Agree with Chief on that... If they are old enough to produce berries, then by all means plant those berries before you top them.
Tops that are not producing berries yet... it should be Ok to top them in early August if you fear they are at risk.
I had a small 3 prong growing here close to my house a few years back, and two trees on the west side of it got hit by lightning and died.
That put that small 3 prong in a situation where all of a sudden, it was getting a lot of direct evening sun. I watched it for a couple years to see what happened.
The first year, the top died in early June, then the next year it died in late June (and had some green berries then)...
I transplanted it after that second year when it died in late june with a big wad of green berries on...
But the thing is this... the top died in June, but it came right back the next spring, and it grew quit a bit during those two years when the top died early. The main reason it grew a lot was all of the extra light it was getting... that made it grow fast, and it got big and stout looking, even though it did die early both years.
Anyway, I know for sure that even as early as early to late June, if a top goes, the root will send up another the next year (considering everything else is Ok with the plant).