As a Business Development Manager, is there any difference in role and responsibilities if I am working in a COMPANY or AGENCY?

I think not different.Because the development and improvement is important for any business

A business development executive is a senior manager tasked with the job of helping his or her business grow and therefore, they are high-level sales professionals.

Their priority is to assist their companies acquire new customers and sell additional products or services to existing ones; this means the role is a crucial one for any business with the ambition to expand or the necessity to diversify its clientele. It also means that effective business development managers are in high demand in nearly every job sector there is, including business-to-business, business-to-customer, and even non-profit organisations.