On September 7, 2008, Federal Housing Finance Agency (FHFA) director James B. Lockhart III announced he had put Fannie Mae and Freddie Mac under the conservatorship of the FHFA (see Federal takeover of Fannie Mae and Freddie Mac). The action has been described as "one of the most sweeping government interventions in private financial markets in decades".
https://en.m.wikipedia.org/wiki/Freddie_Mac
A government-sponsored enterprise (GSE) is a type of financial services corporation created by the United States Congress. Their intended function is to enhance the flow of credit to targeted sectors of the economy
The desired effect of the GSEs is to enhance the availability and reduce the cost of credit to the targeted borrowing sectors primarily by reducing the risk of capital losses to investors
Well known GSEs are the Federal National Mortgage Association, or Fannie Mae, and the Federal Home Loan Mortgage Corporation, or Freddie Mac.
https://en.m.wikipedia.org/wiki/Government-sponsored_enterpr...
Fannie Mae was founded in 1938. Freddie Mac was founded in 1970. Freddie Mac ranks 38 on the Fortune 500, which means it's quite powerful.
One can’t modify a financial instrument like a mortgage to manipulate value of an appreciating immovable non replicating asset like land
Home mortgages aren't really for land per se. They are mostly for fostering the development of specific kinds of buildings on that land. We absolutely routinely "manipulate" what kinds of development we wish to actively encourage. We very often do that via various financial instruments, such as tax breaks, grants and loan guarantee programs.