It's doable if you're patient. You'll get the O2's out and factory downpipes completely disconnected, then have to drop the subframe to squeeze them out towards the back of the car between the subframe and unibody.
Even when the subframe is hanging by the suspension, I still didn't have enough room, so had to pry the subframe down even further to slide the factory downpipes out and new downpipes in.
Took me the better part of a day since it was my first time and I also put in an intercooler.
Cutting isn't necessary or recommended, but if you do, you'll still have to drop the subframe to get the new downpipes in place.