Will replacing B23N20 mosfet with B4227 have problems?
The IRFB4427 has lower ON resistance, but very high input/output capacitances.
In a Class D audio amplifier, I would not replace the IRFB23N20 with it.
Instead, you can use MOSFETs with similar I/O capacities and currents. (IRFB4020, IRFB5620, FQP19N20, RCX200N20)