But the assumptions that have been tacitly made here are to the effect that the regime change can be accomplished only by American boots on the ground in a protracted and bloody war. It occurs to me that there are other options short of inserting the 101 airborne, a measure that Jim Noble rightly points out would never be authorized by Congress.
Again we can arm dissidents, and Kurds, sufficiently so that they can present a mass to the existing regime that must be confronted or the dissidents will simply occupy the principal positions of power and effect change. When the dissidents are confronted militarily on the ground and forced into the open, American airpower comes into play. For this strategy we do not need scarce defense missiles.
We can insert special forces, as we did in initial phases of the Afghanistan invasion, to coordinate with the dissidents and provide them with airpower. We are in the age of drone warfare (regrettably receiving as well as sending) and this should prove an effective air weapon in support of dissidents. One would expect the Revolutionary Guard to be readily destroyed once they are drawn in mass into the open.
These actions, combined with the ongoing economic, electricity, water and fuel crises caused by our blockade and bombing, might be enough to enable a new grassroots, if you will, regime to take hold. So the thesis is that regime change need not come top-down but as a well-nurtured grassroots effort.
Concededly, there is no guarantee that such a new regime will preach only the gospel but we can hope for a Venezuela style volte-face and a new modus vivendi for whatever new regime takes over. These hopes must be balanced against the recognition of the deep and intractable psychological hold Islam has over much of this population. The epiphany will not come cheaply.
The cost of this effort would be minimal bloodshed, reasonable expenditure of conventional weapons by air and by supplying them to Kurds. The major risk is to the Gulf nations that are within range of Iranian missiles fired from behind some God-knows-where mountain that cause serious damage to water and refinery facilities and will no doubt generate backlash among these nations.
At some point, tough decisions have to be made.

“One would expect the Revolutionary Guard to be readily destroyed once they are drawn in mass into the open.“
In my opinion, this should be goal. Drag the IRGC to a situation that they must expose themselves. Remember, they must know that such exposure is certain death. They will have plans to avoid it.
The IRGC isn’t capable, then Regime change is inevitable.