You can swap switch if you want but it needs to be an appropriate switch for the temp of the thermostat.
All I can say is mine were DEFINITELY NOT IN THE MAIN FUSE BOX, there is a FAN SYMBOL, this is for the HEATER FAN.
I do not know if they are wired permanently as std as I never bothered with it, the std wiring.
Keeping the std rad switch is best idea and will cause no problems if all ok.
tabetha