You usually do not need to throw away the entire structure. Update it explicitly so the new objective or constraint becomes part of how you prioritize the remaining analysis.

A case structure is a working map, not a contract. When the problem changes, strong candidates show that they can adapt rather than continuing to follow the original plan mechanically.

If the original goal was revenue growth and the client later requires margins to stay above 20%, you can keep relevant growth branches but add the margin constraint as a screen for each option and deprioritize ideas that violate it.

Pause, restate what changed, explain how it affects your priorities, and revise the structure only as much as needed. Practice treating structures as flexible tools rather than something you present once and never revisit. If useful, this guide on case structure vs. case framework gives more detail.

I think updating the structure is better than pretending the original one still fits.

Restate the new constraint out loud so the interviewer knows you caught it.