Manually migrating app preferences to Yosemite

How I would do it:

1. Create a non-admin throwaway user account.
2. Use Migration Assistant to migrate the Mavericks info into the throwaway account.
3. Look in ~/Library and its sub-folders to see what actually got migrated.

Optional:
4. Try using the throwaway account's migrated settings with the "key app", and see if it works, fails, or is somewhere in between.

5. Start removing things from the throwaway account until the "key app" behaves.
6. If the key app never behaves, create a new throwaway account and migrate nothing to it.
7. Try the key app there.