A modifiable transmitter is used with an operator to control a position of a barrier. The operator includes a controller for comparing radio frequency transmissions received with stored serial numbers so that the controller can move the barrier when a radio frequency transmission matches any one of the stored serial numbers. The transmitter includes a housing that carries an encoder. A function button is carried by the housing, wherein actuation of the button generates in a non-standard way a new serial number that can be learned by the controller to allow the modifiable transmitter to move the barrier by emitting the radio frequency transmission. A restricted access may also be activated to generate a new serial number.