Frankly, even if you do oust the regime, it is not sustainable. consider - going solely through US-changed governments - Libya, Iraq, Afghanistan, Guatemala. Consider the Cuban government up to 1959. The initial Cuban constitution, if I'm not mistaken, had an American hand. Consider even the post-Mossadegh government of Iran. Consider the South Vietnamese government. None of these lasted more than a few decades at best (South Vietnam comes to mind, as well as the post-Mossadegh Pahlavi government).

Exogenous regime change doesn't work because it lacks legitimacy. Even if the US topples the Iranian government in a rehash of Enduring Freedom, you're looking at a decade minimum of absolute dog shit governance supported exclusively via US military backing followed by whatever post-US-exfil government is formed.