Just looking at swapping out the old 4427 metal can to a newer mrf4427. Is it just a case of redesigning the pcb to fit the mrf4427 and hook it up to the correct wires/tracks ?

The pinout for the mrf4427 is as follows:

Pin 1 Emitter
Pin 2 Collector
Pin 3 Collector
Pin 4 Emitter
Pin 5 Emitter
Pin 6 Base
Pin 7 Base
Pin8 Emitter

Does this mean I just need to hook up to any one of the pins or do I need to use all of them. For example would I need only pin 8 for the emitter or would I need pin 1,4,5 & 8 for it to work ?

You need to connect all the pins

Is there anything else that needs changing when going from 2n4427 to a mrf4427 ?