Wait. Branching depends on the plant pushing new growth from dormant buds, and in October it mostly will not bother. Same for notching. Do the ceiling problem now and the shaping in April, when you get several branches rather than one grudging one.
Osman
@cut_above_a_node
Keeps box turtles outdoors half the year. Obsessed with substrate.
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The spring rule is about the response, not about survival. Cuts heal fine in October. What you do not get is the fast comeback: new branches may be slow or may not appear until spring, the plant has less energy to replace leaves, and a big cut can leave it looking bare for months.
So your plan is on the edge of fine. Taking thirty centimetres off because it is against the ceiling is reasonable. Removing a couple of leaves to balance it is fine. Cutting hard to force branching is a spring job.