I had the same question. Here's another: If someone uploads the new Nashville CF3 on Soundmondo, can I download it even if I haven't updated to OS 1.4?

I'm not best suited to answer the initial question. I can cover Soundmondo, however:

Soundmondo relies on the factory samples (Waveforms). You cannot upload any samples to Soundmondo. If you do not have Nashville CF3 samples in your CP, you will not be able to benefit from a Soundmondo user contribution that references the Nashville CF3 (until you update).

Thank you Jason.

Saving a Backup File saves all your current CP88/CP73 Data. You can restore all or some of it. It is your choice. If you select LOAD ALL, naturally all data in the File will overwrite all the new Live Set examples provided in the new firmware. It is highly recommended that directly after loading your new firmware, you play through the provided data... before restoring your Backup data. But recognize you do not have to restore all data in a Backup File, you can load individual Live Set Sounds from within your Backup File (.X9A)

See the Supplementary Manual for details:
You do so by first, select the Live Set slot to which you want to load into...

Loading a specific Live Set Sound from all data files
[MENU] →“File” → Select a file you wish to load from the USB flash drive → “Load Live Set Sound” or “Load All”
You can load a specific “Live Set Sound” from data files (Backup File, Live Set File, Live Set Page File.)

Select a folder containing the file you wish to load, in your case “Backup File”;
You will see a screen with Options to “Load All” or “Live Set Sound“ or “Cancel”
When you select “Load Live Set Sound,” the screen will show you a list from which you can choose the desired “Live Set Sound” to load to your CP.
The file will be loaded to (and overwrites) the currently selected Live Set Sound. (Be sure to select the location before attempting to search for the Live Set Sounds you wish to restore from your Backup File).

When you select “Load All”, all Live Set Sound data contained in the Backup file will be loaded... Load All will overwrite all data in current memory with your data.

Hint: @Rob — the firmware Updater writes the new Waveforms into permanent memory. They are independent of the Live Set Sound programs. Once you do the firmware update the new Waveforms are apart of your instrument’s permanent Wave ROM. Don’t confuse the new Waveforms with programs that use the new Waveforms. When you Save and Load a File, you are saving and loading Live Set Sound programs... only the firmware Updater can INSTALL new Waveforms. When you update, the update routine includes some example programs to give you an idea of what can be done with the new Waveform data... decide if you like, customize it, or make your own.

This option works fast for me to have both my custom made Live Sets and the new Live Sets from a firmware update on my instrument:

Use 2 USB sticks (both have been formatted on your CP).
Before upgrading make a full backup from your CP on USB stick 1.
Now put the firmware upgrade file on USB stick 2 using your computer and perform the upgrade on your CP using this USB stick.
After the upgrade from USB stick 2 is done, switch off your CP, connect USB stick 1 and switch on your CP.
Now navigate to Live Set Page 14 on your CP and save this page to USB stick 1.
Now reload your original full backup file from USB stick 1 in the CP.
Then select an empty Page on your CP and load the previously saved new Page 14 from USB stick into it.
Now you have both your custom Live Sets and the new Live Sets in your CP.

To Bad Mister and Ruud - - -Thank you both for the details. I appreciate it. I hope someday Yamaha comes up with a library manager similar to the "red keyboard" that is easy to use. I own one of those and it's simple to connect to my computer and manage all my performances. I think there is a 3rd party one for Montage. I'm sure it's challenging because Yamaha has so many different keyboards. Just some feedback. Thank you again for your directions!!!!

One thing I think that would help is if the Yamaha clinicians(Like Dom Siglas does for the MODX) would upload a video addressing all of the Load/Save functions similar to the "How to update the CP-88/73 OS" in this video.
There should be more cut and dry video manual content to the operations of this instrument like the once below...

https://www.youtube.com/watch?v=t4ecw8XVgfM&t=62s