It's too tight on the engine side to pull into the rear trunk, at least with the hose on the passenger side still connected. Once that one's loose, you can do it, with some effort.
With respect to the OP's method of cutting the part, somehow that doesn't sit right with me. Esp. when there's a way to do it without having to butcher parts that stay in the car.
For example, My DIY:
Another coolant tank replacement DIY