If you change this resistor, it will operate other RC's that you otherwise couldnt...
It is usually a 200 or 220k between pins 11 and 12 on the TX chip in most controllers. I used a 100k pot with a 150k resistor (gives a range from 150k to 250k).
Different settings would run Z-cars, Thor clones, Thunderfighter clones, even Radioshack trucks!.
You're still sending 27Mhz, but the timing of the data pulses is changed.
There is also a resistor in the car, but its much easier to mod the controller (bigger parts)
This will work on most cars that use the "TX2" in the controllers, the Radioshack trucks ("Hacksaw") and "striker" (buggy) also have this chip, sometimes marked "TS2", but it still works!
This should help more:
http://homepages.paradise.net.nz/bhabbott/tx2rx2.html
Oh, the booster may use a 27.000 Mhz frequency crystal, (usually it's 27.145 Mhz) but that usually isnt too far off to work.