Hi Danny,
I was not aware of this option on the SX models, so thanks for pointing it out.
It is described in the section 'Restoring the Pre-installed Expansion Contents' on page 138 of the downloadable 'Reference Manual' (PO-A0), and confirms that if you use it to restore the pre-loaded packs, the expansion memory will be formatted, deleting whatever is currently installed.
There is a 'Note' which explains that if you want to install the pre-installed packs along with other content of your choice, you would need to make a custom install pack from YEM that includes the pre-installed ones. This would require first importing their CPFs into YEM.
Since it appears that the pre-installed packs use only about 200 MB of the expansion memory, many people will want to make their own 'mixed' install pack, which requires the use of YEM and the CPF downloads.
Regards
Ian