Generally, this kind of distribution mode, which adds several times to the distribution period, is generally called X+Y distribution mode. The so-called X+Y issuance mode refers to coupon rate, where the bond is issued for X+Y years, but at the end of X, the issuer has the right to decide whether to raise the coupon rate of this bond and the extent of the increase. After the issuer announces whether to raise the of this bond and the extent of the increase, investors have the right to choose to register investors for resale in the X interest-bearing year of this bond. Investors who choose to sell all or part of the bonds back to the issuer must register within five working days from the date when the issuer announces the upward adjustment of the coupon rate (this number of days depends on how the relevant bond terms are stipulated, usually five working days); If the investor is not registered, it shall be deemed as continuing to hold the current bonds and accepting or not accepting the above increase.
For what you said, the interest payment cost for the first four years is the bond coupon rate agreed upon when you issued it. In the fourth year, some investors choose to sell bonds back, that is, it is possible to partially or even fully repay the principal. After the resale in the fourth year, if there is no full resale, the interest cost is the newly agreed coupon rate at that time. Generally speaking, in the face of the adjustment of bond coupon rate, bonds issued in this way can only be raised or not, and generally cannot be lowered.