Very little changes - on Earth
Ceres has a mass of slightly over 1% of the moon. As far as Earth is concerned, it is now being orbited by a mass with a barycentre slightly offset from the Moon's centre of mass. But that will change soon because...
Selene is well within the Roche Limit for the moon. So shortly after it arrives in orbit it will disintegrate as a result of the tidal effects from the moon and large parts will probably form a ring system. Eventually orbital perturbations may result in all of the mass in the ring hitting the moon - I look forward to hearing from anyone who can calculate this. So the only effect on earth will be a spectacular ring surrounding the moon in the night sky. The moon will get done over big time by falling rocks.
Do not buy lunar real estate if Selene is on its way!
Edit: time to disintegrate. Wild guesses here, but once Selene's near approach is within the Roche limit it will go pretty quickly, probably in a matter of hours. It will not break down to tiny rocks all at once, it will break into smaller and smaller chunks progressively. As the chunks get closer and closer to those permitted by the Roche limit the rate of disintegration will slow.