No, it is not possible to decrease the size of Earth by increasing its rotational speed while conserving angular momentum. The conservation of angular momentum is a fundamental principle in physics, which states that the total angular momentum of a system remains constant unless acted upon by an external torque.
Angular momentum is the product of rotational inertia (moment of inertia) and angular velocity. The moment of inertia depends on the mass distribution and shape of an object. If we were to increase Earth's rotation speed while keeping its angular momentum constant, the moment of inertia would have to decrease. However, the moment of inertia for a given object is fixed based on its mass distribution and shape. Earth's moment of inertia is determined by its mass, size, and density, and it cannot be changed significantly by altering its rotation speed.
Therefore, increasing Earth's rotational speed would not result in a decrease in its size. The size of the Earth, including its radius and mass, remains constant unless affected by external factors such as geological processes or human activities.