In the late Joseon period, status was no longer entirely fixed at birth. As the state, in effect, sold status and office to refill its coffers, money and grain became routes to change one's standing. The chief instruments of this were the blank warrant (gongmyeongcheop) and the grain-payment policy (napsok).
Gongmyeongcheop — the warrant with a blank name
A gongmyeongcheop (空名帖) was an appointment warrant for office or rank issued with the recipient's name-space left blank. When the treasury ran dry through the Japanese and Manchu invasions, the court issued these documents in advance and handed them over with the name filled in for whoever paid money or grain. Usually they granted not a substantive post but an honorary title or rank — yet even that could bring real benefits such as exemption from military service and treatment "something like a yangban."
Napsok — privileges won by offering grain
The napsok (納粟) policy, to secure finances and relief grain depleted by famine or war, granted those who offered grain or money privileges in return — office, rank, exemption from duty, and sometimes even the manumission (myeoncheon) of a nobi. For commoners and wealthy merchants who had accumulated fortunes, this was a realistic ladder up the social order.
Toppling the class system from within
Such measures helped the immediate finances but shook the very foundations of the class system from within. As word spread that status could be bought with money, the number claiming to be yangban surged while the share of commoners and nobi fell. Add the custom of buying up or forging the genealogies of fallen yangban houses, and the line between "real yangban" and "money-made yangban" grew ever fainter. Behind the fact that so many families today came to hold a yangban's genealogy lies exactly this social mobility of the late Joseon period.