I'm designing a Quadcopter for my project. I've seen a lot of guides that the motor rotational direction should be opposite to each other. My doubt is whether the motor have a variety of CW rotation and CCW rotation, or we should change any other thing in the motor?
Brushless (BLDC) motors are not inherently directional. They can be either clockwise or counter-clockwise, it only needs to be set in the software, or by swapping two of the motor wires on the physical phase output pads of the ESC. The only time a brushless motor will care about rotation is if they have different direction threads on the shaft where the propeller attaches. In that case you want the motors rotating in the direction so that the prop nut tightens against the force on the prop. This is purely functional, not electrical though, if you use nylock nuts, it won't matter if they are all a single thread direction.
Brushed motors however often do have a handedness. Some brushed motors will have slight skew in the magnets that effectively advance the timing when they're running "forward" rather than "reverse" compared to their intended direction. This will result in a faster run speed in the forward direction than the reverse. Also once a brushed motor as been broken in in a particular direction it is often hard on the motor to then run the motor in the other direction. This can result in additional wear on the brushes and a motor that wears out quicker than intended. None of this should be an issue with brushless motors.