Better off taking the cylinder to a hydraulic shop and having the proper torque put on the nut when installing. Their machine will easily remove the nut as well. Remember, Cat lock nuts are designed to be used only once and thrown away after being removed. New nuts are expensive, but not nearly as expensive as a complete hydraulic system cleaning and repair when one comes loose -- as they tend to do more often than not.
Hydraulic cylinder resealing seems like a very easy job, but it isn't. The tools required are big, and expensive. Some manufacturers use different methods of retaining pistons and head glands, which use smaller components, smaller tools, and less torque on the fasteners. But Cat does not.
I've been on the wrong end of way too many home-done hydraulic cylinder repairs, that is, cleaning up someone else's screwup. They nearly always turned out to cost a very great deal more shortly after. This is, I admit, on bigger cylinders, but the same holds basically true on the smaller ones too.
Good Luck!