My radiator fan turns on at 94C (201F) and turns off at 88C (190F). This has never been a problem on or off the track.

While I can tell you how, the question here is; Why do you want a lower temperature for the fan?

 

I'll indulge some.

Lowering the temperature has two main benefits, as I see it:

Makes the fans run more often without doing anything else fancy, which would help with heat soak of my intercooler hex when the car is motionless in grid at autocross. The hex is well forward of the radiator, but intentionally unshrouded/unducted to let air bypass the hex when the 3rd fan isn't running and bypass the radiator as needed when it is running.

Slightly improves knock resistance, and with 91 octane and 9 psi, power is knock limited. I believe this will be much more effective than a lower thermostat temperature, with none of the downsides of earlier thermostat opening.

Other options include forcing the fans on all the time in grid with a pot controlling the speed off of the difference between ambient and intercooler hex temp. But that seems like a lot more work, especially to make sure normal operation isn't inhibited, and to make it automated so I (and co-drivers) don't have to remember to flick a switch.

 

The fans should also turn on with the a/c (at least is most cars, I only ever used my a/c twice in 2 years, then a rock punched through the condenser and I pulled the system)

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I have a lot of experience with different fan control in my 87 supra. I would say that if you DO have an alternative to an aftermarket fan control, go for it because aftermarket controllers just don't seem to have anywhere close the reliability and longevity of the stock systems. The resistor idea is an interesting one and probably worth looking into. I don't know off the top of my head if the spyder fans run off a temp sensor like some older/other toyotas. On those, unplugging the sensor (usually in the radiator at the bottom) has the fans always on (with key ACC), and I imagine a resistor on the sensor could do what you want with a lower "on" temp while not having to have them run constantly (like on a cold start, which isn't helpful). Obviously, if it's an ecu control based off the ecu coolant temp sender, that would be rather a dead-end.