Sorry about the late response to this question. I had read an article on this eons ago, and I wanted to look it before responding. You know how time can catch up on you...

Anyway, I have to humbly ask where you got your information on Philip "announcing" the name-change for Cleopatra. The only mention of Cleopatra as Eurydice that I know of is Arrian 3.6.5. Arrian is actually discussing the return of Harpalos from exile, which was imposed on latter during the reign of Philip when Alexander had become suspicious of Philip, "because he took Eurydike as his wife, and disgraced the mother of Alexander" (my translation). No mention of "Cleopatra" is made, nor an announcement of a name-change. Simply marrying the young Macedonian princess apparently was more than adequate for Philip to insult his estranged wife.

Olympias was not the first wife, yet she had power. The reason for this is certainly something that can and does inspire much discussion (and I wouldn't mind more of it...) But, Olympias does come from Molossia, which neighbors both Upper Macedonian regions and Illyria (let's not forget, Philip's mother stemmed from Illyria, and Audata, his first wife, also came from this area). Although Molossia/Epirus does not receive much discussion in historical dialogues on Macedon, I feel that it merits more attention. Nevertheless, Olympias' position in the royal house was now threatened by a Macedonian bride, whose offspring would be a definite rival to Alexander.

As far as Cleopatra changing her name, Arrian's mention of her as Eurydice has been regarded as a mistake. In fact, Badian argues that the name should definitely be regarded as no more than a good Macedonian name. The only figure we have definite evidence of who changed her name when she ascended to the position of queen was Adea/Eurydice, grandaughter of Philip II, niece of Alexander the Great, wife and niece to Philip Arrhidaeus. Her choice of name must have been conscious of her heritage through Philip: her Illyrian great-grandmother with a Greek name. Cleopatra would have no such reason. Her name was already a respectable Greek/Macedonian name that would cause no conflict in court.

Just as an aside, Eurydice may have held quite a powerful position, at least in the mind of her son. Interesting evidence is popping up in Macedonia, particularly in Vergina where a dedicatory inscription from "Eurydika Sissa" was found in the temple of Eukleia, a major political deity of the region (according to Prof. Drougou, one of the major archaeologists at the site of Vergina). Maybe Olympias had a formidable example to follow, after all (but who simply didn't get much press that we know of...).

For further reading, try E. Badian's "Eurydice", in Adams & Borza, Philip II, Alexander the Great and the Macedonian Heritage (1982): 99-110.