Songs are matched by database ID and/or title (depending on how well the databases match), and the file used by the song is matched by name. If you let MobileSheets manages your files and you don't create a subdirectory per song (these are settings under Settings->Storage), then usually most libray synchronizations are handled smoothly. I detect file differences already by using a hash, as that hash is cached in the database to make it easier to determine when files have actually changed and need to be transferred.
I don't really think it needs to be any more complex than this - just keep the file names the same and the sync should match things up properly. I know you are saying you are renaming the files - that's not going to work well if you are using a two-way sync. If you want to rename the files, go through every song in MobileSheets that you want to modify, edit in the song editor, go to the Files tab, tap the three dots next to the file, select "Rename file", and once you've renamed all the files, when you sync, you must use a one-way sync. Do not use a two-way sync or this will create havoc. Now push the changes from one device to the cloud (set the sync type to "Update Folder") When it completes, go to the other device, set the sync type to "Update Device" and pull the changes from the cloud. This will force both devices to match perfectly and there won't be any conflicts, and all the renamed files will be handled appropriately.
Mike
I don't really think it needs to be any more complex than this - just keep the file names the same and the sync should match things up properly. I know you are saying you are renaming the files - that's not going to work well if you are using a two-way sync. If you want to rename the files, go through every song in MobileSheets that you want to modify, edit in the song editor, go to the Files tab, tap the three dots next to the file, select "Rename file", and once you've renamed all the files, when you sync, you must use a one-way sync. Do not use a two-way sync or this will create havoc. Now push the changes from one device to the cloud (set the sync type to "Update Folder") When it completes, go to the other device, set the sync type to "Update Device" and pull the changes from the cloud. This will force both devices to match perfectly and there won't be any conflicts, and all the renamed files will be handled appropriately.
Mike