"If a fish could walk on land, would it still be a fish?"
Yes. Yes is the answer. They don't switch clades the instant their fins touch land or anything. That'd be stupid.
And "fish" is a paraphyletic
group that doesn't make much sense in light of evolution since it includes a common ancestor and some but not all of its descendents. Rephrased in accurate terminology the question becomes "If a vertebrate could walk on land, would it still be a vertebrate?". And that answer is a resounding duh.