First of all, this is a huge decision. Do not take my words on this or anyone else's. You are the only person who has to make a decision and live with that for at least a couple of years. So do not take a hasty decision.
Now let us deal with your issue. Your issue has two parts:
a) A subject with a foundational background: It seems that you have a sound background in accounting and it will take you less time to prepare for it. That is true; it will take you a little less time to prepare for accounting and you can utilize this time to study other subjects such as current affairs and Pakistan affairs. However, you should keep a couple of things in mind. Firstly, having a foundational or even advanced knowledge in a subject does not necessarily mean that you will score high in the exam. Secondly, you might think that you have previous knowledge about accounts; you might not study as harder as it is required and in the end, it might not be as fruitful as you would have liked. Beware of these two things and you will do absolutely fine in accounts ( the Second point involves psychological perspective, I hope that I have made myself clear).
b) Overlapping Subject: It is also true that International Relations overlaps with Pakistan Affairs in general and with Current Affairs in particular. However, International Relations is a very dynamic subject and a bulk of foundational work would be required to get a hand of it. You have to keep yourself up to date with every resource available to you keeping in mind the foundational work of IR. So if you know the foundational work and learn the dynamics of IR, you will get a hand of IR and CA and Pakistan Affairs would become by-products.
In the end, If you choose accounts then you have to work hard for CA and Pakistan Affairs and if you to select IR then you have to work hard for IR. The amount of work will be equal. So chose the subject which is more interesting for you. The choice is YOURS.