Yes, you can add pepper. Not salt though. You can also add a little chilli powder, or mixed herbs (preferably fresh otherwise check ingredients). You can have up to 1g a day in curry powder with caution. If you do find that any of the above cause hunger, stop immediately.
Most should be fine. The curry powder can cause a problem in a very few people.
You can add cinnamon and nutmeg too. Though most people would consider cinnamon to be for sweet dishes/meals, I often add it to savoury dishes. Love the stuff.