This is not needed on SR Piaggio engines, we believe it may be for the older Hyper 1 engines.

Yes, you can replace just the seal without splitting the engine but it is fiddly.There is a small black plastic pipe by the flywheel and if you remove it you can access the water pump impeller with a 8mm T-bar to unscrew the shaft (hold the shaft still on the variator side).It is left-hand thread so you need to turn it the opposite way to the way you would normally turn to unscrewThen you need this seal kit but you can't replace the impeller without splitting the engine (not normally necessary).
Make sure to use coolant otherwise the seal wears quickly with plain water.
An electric pump makes most sense where the impeller is broken and you don't want to strip the engine or if you are going for ultimate performance (an electric pump slightly increases performance because of the small drag of the original waterpump). You would need to replace the seal anyway otherwise it will still leak.