I would suggest that perhaps you want to be an "Environment Design(er)".
One of my profs at Purdue set himself up within an architectural firm that specialized in hospitality/restaurant projects; his niche was taking care the development of miscellaneous furniture, and hardware that was beyond the scope of an "interior" designer. He later went off on his own.
If I'd been smarter, I would have followed him to Boulder in '84 when he invited me to become his "nut's & bolts" vendor liaison guy .... but I digress.
The goal is kind of two-fold: first fix research-identified efficiency problems in the existing business model, then diversify services to increase foot-traffic and grow a clientele base. Somewhere in between those, elements of the store will be thoughtfully designed to help achieve those goals.
There have been several shows on Discovery dealing with the "convenience store" market; how stores are laid out to direct customers to specific areas of the store; even to the point of which side of the door is hinged on a "soft drink" case to cause customers to proceed in a desired direction. Who designs convenience stores, and what areas of study do they pursue ... probably not too hard to find out, if you're motivated.