This spell isn't modal. When it resolves, it will destroy the target if it's a creature or an artifact, even if it changed from one to the other between targeting and resolution.

Putrefy : règles, fonctionnement et interactions (MTG)

Putrefy is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Destroy target artifact or creature. It can't be regenerated.

How it works : Putrefy

Original English text — Wizards of the Coast / Scryfall

#1February 1, 2006· Wizards of the Coast
This spell isn't modal. When it resolves, it will destroy the target if it's a creature or an artifact, even if it changed from one to the other between targeting and resolution.
No other card is named in this ruling.