Deferred principal must be repaid pursuant to the terms of the loan mod agreement.
The deferred principal of a mortgage under a modification agreement has to be repaid in accordance with the terms of the modification agreement. Without reading it, I can't state with 100% positivity but usually the deferred portion does not need to be repaid as arrears in a chapter 13 bankruptcy. Usually the deferred portion is paid at the time the loan is paid off by sale or at the end of it's term, or when the mortgagor dies.