Considering how things proceeded in Nicaragua after the Contras failed IOTL, it seems like the entire enterprise was just one of horror and waste. Ending that period earlier (or even better, never funding it to begin with) would be a pure good, and quite possibly with a similar political result to OTL. If you want Ortega out, carrot/stick aid/sanctions seem to have been wholly successful on their own. If anything, funding armed resistance was a drag on that process.
I don't know how you keep Ortega in power, if that's your goal.
In terms of Iran, I defer to someone with more expertise. Did the arms sales make much of a difference in the Iran-Iraq War? Looks like <2000 anti-tank missiles and a few hundred AA missiles? Probably not much of a difference.
Without that engagement with Iran, are regional geopolitics affected at all?