Against the rules....for most large outboards. That is why you don't see them for sale on line. And the one that does sell them, you still have to have a authorized dealer install in order for the warranty to comply. The days of sending in a paper for warranty have long gone. It's all done thru the dealer online.
Now.....That is not to say you "May" find a dealer that will let you do a lot and they make the final hookup.