I have never scraped a wet horn, but I might give it a try.
I prefer to use rasps and files for roughing in, but do resort to scraping for final finish.
If my memory is correct, Roland Cadle claims that the only reason to boil a horn in water is to reconstitute the lignins in the horn prior to heating in hot oil. Horns less than a year old shouldn't need boiling in water.
Soaking in water might do the same thing. To be honest, I dunno.
He goes on to say that boiling in water doesn't get the horn hot enough to release the memory in the horn. It takes heating to no more than 350 degrees to release the memory, so's it won't want return to its original shape.
J.D.