I have tried repotting pines late summer, when night temps finally start dropping into low 60's, for me after Aug 15, for you maybe middle or late September. My succes equals my spring success, which is not 100% but is pretty good. I do provide winter cold protection for these trees, but so far, so good. Usually JBP.
Tom Dimig container from the early 90's...this is first "nice" container I ever purchased!...$75 and I had to save for weeks...I wish Tom was still making pots!!