Originally posted by Leigh Witchel
Nureyev is one who has done this. My guess is the choreographic reason is to bring the number of fairies to seven so that the Lilac Fairy (or in Nureyev's case, the dancer who danced what we consider her variation - the Lilac Fairy was entirely a mime role) could be central.
Actually, Leigh, apparently Marie Petipa danced the original Lilac Fairy variation. Nureyev's production was one of those that reacted to the release of a photo from the Maryinsky archives showing Marussia in heeled shoes and a chemise-shift that would have been impossible to do the Prologue variation in. What nobody at the time knew was that that was a picture of her in the Spell scene (Act I) and later, when she didn't have any dancing to speak of. And all those productions changed just on the strength of one uninterpreted photograph! Makes you believe in the power of archives!;)