Oh yes the Muslim world would be livid, so if there are attacks and Iran responds by blowing up nearby Muslims, would that convince Israel that it may be worth joining an alliance?
With the rest of the world, what do you mean it won't be accepted easily? That they would think it's fake? What if every Iranian they talk to says they all received a vision from Ahura Mazda and they think this is proof that Zoroastrianism is the correct faith?
On the last point definitely, at least at 1st. Its such a radical change that a lot of people would be dubious about the conversion. Coupled with the deep mistrust that has developed with Iran since 1979, especially in the US. Some of the more conspiratorial might also think its a way of getting out of western sanctions for instance. Even if say some of the former top mullahs are now broadcasting that they were wrong, Allah is a false god and Zoroastrianism is the true faith. - Which is going to enrage their neighbours a lot more.
Israel would probably seek a low profile on the issue for the moment. After all their suffered a lot from the Iranian clerical region and its attacks so there would be a good degree of mistrust and suspicion of the conversion. Plus if Iran is involved in a major shooting war with several neighbours they would probably prefer to keep away from that and let the two groups bled each other out. You could see some back door connections but it would only been in a crisis for Israel or when [ or if] the situation calms down and people accept the conversion is true that they would seek friendship. Possibly not even then as it would alienate their Muslim neighbours again.
Possibly the most likely allies for the new Iran might be Armenia - with a common dispute with Azerbaijan - Iran now having an even more unhappy Azeri minority unless its also converted, Russia or China. Either of the latter however are unlikely to prompt good relations with the west.
The other issue would be the attitude of the new Iran to other neighbours. If its as religiously extreme as the Muslim version with persecution of minorities, or if their all also been converted of other religions generally and say starts converting mosques into fire temples its going to cause concern in the west as well as the Muslim world. If their a more general live and let live Muslim anger will be somewhat less, but still high but their likely to have better relations with the west and possibly other parts of the world.
