I know for sure that this happened regularly in older stores - they simply knocked walls out between the main store and the food store - not always was the operator Kmart:
Danville, IL: was built 1963 in an odd L shape. The last grocery operator there was Kroger. Store was expanded into the grocery, but was home improvement only in the grocery area.
Tyler, TX: also an early build. Straight store, but the wall was knocked down between the two stores before 1980.
Alexandria, LA: first Kmart in LA. Wall simply knocked down.
Dallas, TX RL Thornton Freeway: also early build where the wall was knocked down
Gadsden, AL: later build with the same results.
I could go on, but you get the point.