It is intended to be a factory fit option.
But, my understanding is that it could be, but it is only suitable for a manual car.
The changes are not quite so extensive as those to the turbo, but still require a new inlet manifold, new exhaust manifold, new inlet side camshafts with higher lift and larger wider ports on the inlet side, whether this means the inlet manifold, or larger valves which would require a new head, I'm not sure.
These bits could all be bolted on, if you can actually order them.
I suspect you might struggle to get them from anyone other than Porsche themselves, who may want to limit availability to keep it a factory fit option, but if they will sell them, the prices will be high.
The Porsche website (configurator) is not working at the moment, but I seem to remember the factory option price was 5K or more. Aftermarket, it would be more just for the parts, and you need to add quite a few hours labour.
(It's not suitable for GT3/TT, but perhaps you have other plans.)
One of the other GT3 members, Kevin Cooke, had it on his C4S I seem to remember, so he may be able to help you.
My understanding is that the benefits are only really above 6500 rpm, where you get more power. This is useful on the track, but not worth the money on the road.