Hi Rebecca - I haven't actually done this, however the approach I would take would be to use the "Export Star Schema" functionality in the Spend Visibility Manager console for your back-up on external storage (can be done by date). If you need it for legal, you can always import it back in, or import it on a non-Production environment for the audit.
To get rid of the data in Analysis, I would just leverage the existing Analysis Delete load functionality. It's a purge, not a set Active to false. For example, you could copy or extend the POLineDelete to grab anything with a data older that 2010.