As per my knowledge, the workspace of a manipulator can be determined if one knows the forward and inverse kinematics. But is it possible that the workspace of the manipulator can change after considering the effects of dynamics?
In other words, can I determine the workspace of a manipulator only from its kinematic model? Or do I need to consider the dynamic model as well?
The workspace of a manipulator is strictly determined by its kinematics. Since kinematics only consider the geometry of motion, without regard to forces and torques needed to accomplish tasks, you need the dynamics (and controls) to determine what motion profiles are achievable within the workspace. But those dynamics do nothing to determine the workspace itself.
I think it depends on how much useful life you want to obtain from the robot.
It is possible that a perfectly acceptable kinematic solution within your target workspace without regard to dynamics could result in moments, velocities or accelerations that could cause one or more actuators to operate well beyond their rated torques. By not imposing any dynamic constraints on your workspace you are basically risking unnecessary damage to your manipulator's hardware.