This also must be done when going for an affluent fame type, as it requires a level of 7 in order to do. Not only must you be a high level, but you must have 99 of each resource as well in order to use the special in which you purchase the imperial seal.
I'd suggest pairing this one up with the "Yes, I can" trophy, as you simply have to do this very same thing after starting as a common free officer and saving yourself a playthrough.