Can a supervisor request student to change topic completely after acceptance into University????? A complete change from one area of research to another?????

Are we talking a whole other department? Or a similar topic in the same research area? Because the latter is not that unusual - in the lab-based sciences anyway. And sometimes a change of direction happens during a project too. Maybe speak to your supervisor to discuss the changes, and the reasons for them? They may be choosing something that is better for you in the long run!

It is possible. If the professor feels that the previous topic will not produce enough research material or if the research output might not be what the department was looking for. You can expect such changes in any university.

I think that often supervisors will use a 'catchy' topic to gain funding, and then change the topic to what they actually want later. research councils are pretty slack on checking whether the original topic is the same as they requested cash for.