Dear Mr. Suraj,
A government servant has to surely obtain his employer's (controlling officer) permission for applying to another Government job, whether or not you want to take any benefit of the past service. If you do not do that, disciplinary action can be taken against you. Further after passing the examination, you will not be permitted to join the post unless you get relief order from your past employer. Government department's do not stop any one from applying for any other post / examination through proper channel. So instead of thinking in short cut methods, right royally apply through your department for the examination, clear the same and join higher post.
Best of luck.