Limiting motor speed?

Is there any way I can program the vex motors to run slower than max forward and max reverse if I assign the motors to two buttons? (Such as channel 6 on the controller) I want to try to limit the speed to give me more control over it even though I already have it geared down. I’m using the 2 motor tank style so I can’t use one of the joysticks to control it. Is there a command or something to limit the speeds to something lower?

**To slow a motor down using a button, just change the value of the appropriate pwm. Values can range from 0 to 254, where 127 is neutral.
The follow code is an example:

pwm05 = 0x7F;           //Handle Channel 5 button
    pwm05 = 177;     //Slow down the (when in reverse)
else if (PWM_in5 > BUTTON_FWD_THRESH)
    pwm05 = 77;         //Slow down the (when in forwared)