It will not damage the plant, but there is a slight possibility that under severe stress the leaves & flowers higher up might show wilt-like appearance. If so, them prune slightly below the affected parts, or if you want to , back to the split.

My Marie Boisselot (type 2) is 6-7 years old and has lots of split stems, but this hasn't prevented her climbing into the huge lilac clump to rise above it to approx 10 feet, with no signs of distress.

My Polish Spirit (type 3) had been planted almost as long closer to the lilac roots, and had done poorly, but last year showed a good growth of stem & leaves, but still no flowers. I decided that since it liked the sun conditions there, I would dig it up & pot in a large tub in the same spot. Some of the brittle stems did split in the process, and I buried the splits in the soil in hopes that the adjacent leaf nodes would root to produce a new plant. I haven't dug around to see if this has happened yet, but the old stem end that I kept above the soil line has new leaves coming up at the same rate as the unbroken stems. Still too early for flower buds here, but I hope to finally see some.

Marie