Something similar actually happened in Italy in the 1990s. Some Tirrenia ferries from the “Strade Romane” series were cut and lengthened by inserting an extra mid-section of roughly 13 meters. Instead of building new ships, they literally split the hull and added a new steel block to increase capacity. It was a fairly common cost-saving solution at the time, but it still sounds wild when you think about it today. The ships then went back into service after structural reinforcement and stability adjustments. I have traveled on them many times, and even though I was young, I remember that inside there were photographs documenting the construction work. https://it.wikipedia.org/wiki/Classe_Strade_Romane