What is the equivalent of "冒昧打扰" in English?
I would say it is equivalent to "Excuse me" in context when you need ask some people for help or a favor.

冒昧打扰, 请问去这个车站怎么走？ - Excuse me, do you know how to get to this train station?

but 冒昧打扰 is kind of formal, we usually just say "打扰一下" in everyday life.