Yes, you may replace the MOSFET, that’s basically almost the same transistor only in a Isolated Package. The continuous drain current = 8-9A, that’s lower than 12A for the original IRF9Z34 , but in this application the MOSFET switching the power supply towards the target circuit is overrated, MOSFET used only to achieve the lowest possible voltage-drop on the power line.
Anyway, if the target circuit consumes no more than 100mA you may to use a lower power, see for example BS250.