Iran wants the regime very much to hunker down and see it through, lebanon is of utterly no significance at all I think your definion is somewhat narrow and coloured by the cold war, I guess you're thinking Iran, [nasser's] Egypt, Guatemala etc but actually they came about as a result of a fear of loss of American support that bolstered their power base rather than any issues with nationalisation per se. Historically coups are done by parts of the army in a position to do so (think majors and colonels, generals less so because they usually have vested interest in the current establishment) out of a combination of self interest and an idea of 'what's best for the state' which may very well include a combination of carrot and stick by external influences. They may well be driven by political philosophy, or more likely antoganism to the established philosophy or more realistically fears of what philosphy may become established, think the nationalist coup in Spain in '36 fearing communism/anarchism or even Egypt's recent coup fearing moves to fundamental islamism. In terms of Syria I don't think it would take much to persuade those in direct control of divisions well placed to do, that th regime is extremely bad for the country and the potential rewards of taking over are worth taking. I mean the country is edging towards a permanent division and the economy is utterly fucked even if parts of Damascus and the middle classes reamin otherwise unscarred by war. It would probably involve a leap of faith that moving the locus of Syrian spheres toward turkey/US away from IRan/Russia, and that may be a leap too far. Though thinkikng about it I wonder if it would actually be a solution that Russia might encourage, if getting rid of an intransigent figurehead but keeping the establishment staus quo might solve the problems at a stroke whilst being acceptable to them too.