Certain joint properties can be changed and set even after the creation of the joint. There are a number of constants that can be used in this function and they can be found here: Physics Joint Constants.
physics_joint_set_value(joint, field, value)
|joint||The index of the joint that you wish to change|
|field||The constant for the joint property that you wish to change|
|value||The new value for the joint property|
phy_joint_max_motor_torque) < 2
physics_joint_set_value(revJoint, phy_joint_max_motor_torque, 2);
The above code checks to see if the joints maximum motor torque is set to less than 2 and if it is it then sets it to 2.