We are currently designing a class modification methodology for GemStone. We describe the current status of the design. We choose from two basic approaches and then introduce those aspects of GemStone necessary for an understanding of the paper. After defining a set of invariants for GemStone databases, we discuss specific class modification operations in terms of maintaining these invariants. We next discuss several issues that impact class modification. These issues include concurrency and authorization, and lead to difficult choices.