A shrink-wrap schema is a well-crafted, complete, global schema that represents an application. A concept schema is a subset of the shrink-wrap schema that addresses one particular point of view in an application. We define schema modification operations to customize each concept schema, to match the designer's perception of the application. We maintain the integrated, customized user schema. We enforce consistency checks to provide feedback to the designer about interactions among the concept schemas. We embody these mechanisms in an interactive system that aids in shrink-wrap schema-based design. The shrink-wrap schema approach promotes reuse of past design efforts; prior approaches to schema reuse did not attempt to reuse an entire schema nor did they focus on local customization. The focus of this paper is on the definition of concept schemas and their corresponding modification operations.