Mostly, the suspension brakes in. Surround starches, spider becomes more elastic.
You don't have to take my word for it. Read “Measuring Loudspeakers” by D'Appolito and find the paragraph on brake in period. I have measured a differences in the driver performance myself after 24hours of MLS. There's usually a slight change in FS and FR of the driver. Again, it's more important to a designer then a consumer.
Tweeters are the same situation but to less extend. Remember, Loudspeaker cone is an electromechanical system.