How do I use iTunes LP with different song files?

Question

I have an iTunes LP that I want to be able to use with alternate versions of the song files (higher/lower bitrate), but the iTunes LP isn't able to play the new versions of the files. What's missing?

Answer 1

After some poking around and searching more, I found the answer, and it lies in ordinarily invisible data and metadata.

The upshot is that iTunes LP primarily references files based on their XID. In order to assign the correct XIDs to the new files in iTunes, do the following (on a Mac):

1. Right-click (control-click) the .itlp file in Finder, and Show Package Contents
2. Open the manifest.xml file in a text editor (TextEdit is fine)
3. Open a Terminal window and enter the command defaults write com.apple.iTunes booklet-authoring-mode 1
4. Quit and relaunch iTunes
5. Find the <library_item> tag in the XML file for the first song, and copy its xid attribute (the part between the quotation marks)
6. Right-click (control-click) the first song in iTunes, and Get Info
7. Because of step 3, the Grouping field will have changed to XID. Paste the XID copied in step 5 into this field
8. Repeat steps 5 and 7 for each track (if they're listed sequentially in iTunes, you can use the "Next" button in the Get Info window to accomplish this more quickly
9. Once you've assigned the XIDs for all tracks, run the iTunes LP file and everything should work
10. Quit iTunes
11. Open the Terminal window from before and enter the command defaults write com.apple.iTunes booklet-authoring-mode 0
12. Quit Terminal
13. Reopen iTunes, and you're all set and back to normal

(These instructions were gathered from Apple documentation here and here)