How to recover changed links in Safari Favorites?

If Safari Favourites have been changed unexpectedly, you can try restoring an earlier automatically archived version of your Safari bookmarks through iCloud. 

Go to iCloud Data Recovery, sign in, select Restore Bookmarks, and choose an archived version from before the changes. 

Apple says the current version is archived before restoration, so you can return to it if necessary. (Apple Support)

If you are using Safari on a Mac, you can also edit a Favourites URL directly through Bookmarks > Edit Bookmarks. 

Apple documents that a bookmark's website address (URL) can be edited. (Apple Support)

For future protection, Safari on Mac can export your browsing data, including bookmarks, to a file. (Apple Support)

To recover and revert your altered links in Safari, you can use  iCloud recovery to roll back your entire bookmark and favorite library to a timestamped backup from before the issue occurred.