If a controversial change to accounting standards is implemented as planned in January, accounting for mortgage-backed securities could be a “nightmare” according to analysts. The Financial Accounting Standards Board is set to change the way prepayments are accounted for, which could signifi-cantly impact MBS, CMOs and even loan rates.FASB plans to implement FAS 155 in January to amend FAS 133 and 140. While the previous accounting standards exempted MBS, the current version of FAS 155 does not, which worries...