Replacing the regulator *might* require disconnecting the fuel lines, but it depends on how the lines are attached. If the lines are easily disconnected from the regulator with reusable fittings (like quick-connect type fittings), then you likely won't need new lines. However, if the lines are hard lines and the regulator is part of the fuel line itself, or if the fittings are damaged during removal, then yes, you may need new fuel lines.
Before starting any work, it's crucial to relieve the fuel pressure in the system to avoid injury or fire. Consult your vehicle's repair manual for the correct procedure.