All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger.
You are asking about something expected in the future, which you may or may not attain. Why not instead ask about a judgment on what you want to do now, namely appointing someone to sit in for your exams on your behalf, whether this is permissible for you to do it so you do it, or whether it is forbidden for you to do it, so you refrain from doing it and start looking for legitimate means to study or work.
In any case, another person attending at the exams in your country on your behalf (as if the person attending is you) so that you will present a certificate proving that you are studying in your country and the reality is otherwise, all this is fraud, deception and cheating, which are forbidden, and what you mentioned is not a necessity which entitles you to do this. So, you must fear Allaah and refrain from doing this.
If someone fears Allaah, Allaah will spare him of his trouble, and He will facilitate matters for him and provide for him from sources he never expects.
As for your question regarding what you will earn from your job, then a judgment on this depends on the permissibility of the work itself, the employee having knowledge about it and his performing the job as required. For more benefit, please refer to Fatwa 84658.
Allaah Knows best.