When I modified an old 9'6" #5-6 IM 6 blank (I shortened the butt section about 5" one foot from the "ferrule" and the tip section the same amount from the tip down) to make a longish, but light, spinning rod dedicated to pendulum casting small Mepps's for sea-run browns on my overgrown stream, I found much advise in this article:
https://www.rodbuilding.org/library/repair-oquinn.htmlBtw, people told me it was impossible to repair/modify graphite rods and get it durable, but so far it has hold up, maybe because no fish have been heavier than about 4 Pounds.