2. insurgency
Supporting an insurgency of minority or opposition groups.
Iran is a multi-ethnic state, Persians little more than half of it. Kurds, Baluchs, Arabs, Azeris and others populate the country. Khameini has Azeri origins for example. It might be possible to turn against the regime one or many. Kurds are a convenient example - but these days I heard (on Caspian Report) that even Azeris could be played against the government.
Beyond them they could form external opposition groups from Iranian expats ("punctuated military operations" >>54316), or prop up the National Council of Resistance of Iran (NCRI) or the Mujahedin-e Khalq (MEK). Or anyone else who is willing.
One real question: could they initiate a regime change? While a revolution certainly does that if successful, but an insurgency might be better for distraction, or as an option to put pressure on in a "persuasion" policy.
3. coup
A timeless classic. Probably this has the shortest chapter. Would be most convenient for the US if the Iranian military couped the regime. But the US has no good way in to engineer it. As here I wrote >>54316 based on the US Foreign Policy in Perspective, this is pretty much impossible.
Imagine what would an Iranian officer (a colonel or a general perhaps) would think if a stranger approached him and hinted that he should do a coup. Will he think:
>yeah this is a legit CIA agent I should start organizing
or:
>fuck me, the regime is testing my loyalty, best report this highly irregular event, and pray to Allah I won't be taken in the middle of the night
?
Exactly.