You can disable the fuel by pinching the fuel line to the pump or removing it from the carb. You can then ground the coil wire to disable the ignition. If you are planning to replace the spark plugs, remove the originals and do not install the replacements. Add a little oil into each cylinder via the spark plug holes.
With a fully charged battery the engine can be cranked until oil pressure is developed and clean oil is being pumped everywhere. That should allow the rings to move in their grooves since there will be no compression. Once you are satisfied there are no unusual mechanical noises and the excess oil is blown clear from the cylinders, the new plugs can be installed and fresh fuel introduced.