No. By definition, a walk-off home run is a home run that ends the game. Therefore, a walk-off home run can only be hit by the home team in the bottom half of an inning.

It's called a pinch-hit walk-off home run.

A walk-off home run is a home run that ends the game. It must be the run that gives the home team the lead in the final inning of the game.

A walk off home run occurs when a player on the home team hits a home run and the visitors walk off the field because it is officially the last play of that game. For example, in the 1988 World Series, Kirk Gibson, a player on the Los Angeles Dodgers hit a walk off home run to end that game in the series.

A walk-off home run is a home run which ends the game. This is a phrase that has only recently entered the baseball lexicon, believed to have been started by Dennis Eckersley of the Oakland Athletics after Kirk Gibson hit a home run off of him in the bottom of the ninth inning in Game 1 of the 1988 World Series to win the game. If the home team hits a home run to win the game in the 9th or an extra inning, both teams walk off the field since the game is over.
A walk-off home run is a home run in the bottom of the last inning that ends the game. A walk-off home run is a home run that ends the game. It must be a home run that gives the home team the lead in the bottom of the 9th inning or the bottom of any extra inning. It is called a "walk-off" home run because the teams walk off the field immediately afterward.