Dear @Asad,
a heartly welcome from me, too, and thanks for the interesting question.
First of all, to provide you and all our readers with a better understanding of the following, some remarks about §16a immigration act. This relatively new paragraph is part of the skilled workers immigration package aimed at attracting and retaining skilled employees. This unfortunately entails very limited options to change your residency status.
As outlined in the procedural notes of the Berlin immigration authority, a status change is possible for the following purposes only: 1. Change to a qualified vocational training (highly improbable in your case, as I assume that you're undergoing a qualified three years training at present)
2. Change to an employment as a skilled worker/specialist (which would be possible on the basis of your BA degree)
3. Change to an employment requiring distinct professional practical knowledge (also not excluded for you, just one example: Provided you've been working with MSAPPs during your studies and find an employer seeking exactly a young specialist for hand-tailored MSApps adjustments).
If you wish to pursuit the MA-programme, it would be necessary to apply for a student visa at the German embassy in Pakistan. Please note that there are some prerequisites to be met, such as a blocked account, alternatively a Declaration of Commitment, which might be the highest hurdle.
I hope I could contribute to clarification. Please don't hesitate to come back to us with further questions.
Kind regards,
mbeon-Christine