Andreas Christopheros, 29, was attacked at his Truro home by David Phillips, 49, from Hastings in Sussex.
Phillips admitted assault causing grievous bodily harm with intent and was given a life term in 2015.
Judges imposed a 16-year sentence and said he will be eligible for parole after he has served eight.
Mr Justice Wyn Williams told the court: "We acknowledge that this crime involved a great deal of planning and a great deal of determination to carry through."
He ruled that Phillips, who carried out the attack in a case of mistaken identity, had wrongly been condemned as a highly dangerous man from whom the public would need future protection.
"We are therefore forced to conclude that this life sentence was not justified and must be quashed," the judge ruled.
A man who carried out an acid attack leaving his victim blind in one eye has had his sentence cut by the Court of Appeal.