You can't just slacken off the two bar pinch bolts and rotate the whole bar. The inner of the two pinch bolts passes through a groove in the bar which prohibits bar rotation - also stops the bar falling out if the pinch bolts slacken off for some reason.
Unbolt the brake master from the bar, then either pull out the locating pin (good luck and you'll need vice grips at the least!!) or cut it off and file flush with the bar. Then simply bolt the brake master back on in the position of your choice.
15mins tops