You're only able to have one ordinance active at a time (which I believe Isabelle states when you unlock the ability). They cost 20,000 bells to enact, and they do not go into effect until the day after you enact them.
The Music Box
The Music Box is actually a family of furniture items, only obtainable by the method you mentioned. Like all other furniture from Cyrus, it is not possible to take one of his products apart into the original materials/furnitures used to make it.
When Cyrus creates the Music Box, the result is a colourful version of the Giant Clam Shell that, whenever opened, will play a little music-box-like version of your song, before closing shut once more.
You can think of the Music Box as a larger, physical, standalone counterpart of the song used to create it, as the Music Box will retain its name when created.
Additional Copies of Music
As for obtaining another copy of the song, if you have access to the Timmy & Tommy Shopping Catalog from upgrading the Nooklings' shop at least once, you'll notice that there is a category in the catalog for music.
Although you cannot order Music Boxes this way, all of the K.K. records you have ever received or will receive in the future will be recorded in the catalog. Each of these records can simply be ordered from the catalog for 3,200 bells.
Therefore, by purchasing your additional copies from the catalog, you are free to request new pieces of music from K.K.Slider each week.
Best Answer
The Early Bird and Night Owl extend the hours, not shift them. So using the Early Bird ordinance will result in all shops opening 3-4 hours earlier (depends on the shop) and closing at the regular time. The night Owl ordinance will result in all shops open at regular time, and closing 3-4 hours later.