By Kenneth R. Harney harneycolumn@gmail.comWASHINGTON — A key policy change by mortgage giant Fannie Mae that offered homeownership to thousands of new buyers — many of them minorities — could face significant cutbacks. The reason: Private mortgage insurers are rethinking their decisions to participate. The change, which took effect last July, allowed borrowers with debt-to-income (DTI) ratios as high as 50 percent to obtain low-down-payment mortgages.Read more on NewsOK.com