With roughly $900 billion of mortgage servicing rights changing hands since October (or about to), and more on the way, Fannie Mae and Freddie Mac will be busy in the months ahead approving the transfer of MSRs.Much of the MSR product being sold by Bank of America in its recent deal with Nationstar Mortgage and Walter Investment Management Corp. is tied to loans guaranteed by Fannie, Freddie and Ginnie Mae.Servicing advisors who’ve worked with the GSEs note that their approval on a servicing sale is hardly a routine matter, especially if the product has high delinquencies, which is the case with some of the BofA receivables.