I have a Black Hamburg vine which is rooted in the garden but growing in a long conservatory. Vine is about 20 yrs old and has 2 main branches, each over 30ft in length. Vine is healthy and produces a good crop but has now got too big. Can I cut the two main branches back to say 10 ft without ruining the vine and, if so, how/when best to do it? If not possible to cut back, can it be transplanted into another conservatory without too much damage?