If a bond has an early redemption right (put option), is the principal guaranteed?

No. An early redemption right is merely the investor's right to demand repayment at set times; to actually get the money back, the issuer must be able to repay at that point.

KOFIA guidelines provide that, when valuing mezzanine securities held by a fund, a C rating is applied across the board if there is no valid credit rating and the credit risk grade cannot be estimated, and in that case the early redemption right is treated as practically impossible to perform and is not reflected in the fair value. In other words, the value of a put option ultimately depends on the issuer's creditworthiness.