Answer
While rehost changes only the location, replatform adjusts parts of the environment to improve operational efficiency, with the goal being optimization rather than redesign. A redesign updates the visual presence of a website and could involve moving elements around to create the best experience, but these projects can be limited in scope and have the tendency to morph into a rebuild as changing the design often means changing the underlying code. Replatforming and refactoring both improve what already exists, while rebuilding creates something new; if the business roadmap requires the application to do things it fundamentally cannot do in its current form or scale in ways its architecture cannot support, then improving what exists will not get you there.
Replatforming carries the lowest risk but the shallowest ceiling, while refactoring carries moderate risk but can unlock significant capacity and performance improvements. The most expensive route is a rebuild, which provides the most freedom, whereas a redesign or replatform may be cheaper and faster but are limited in what they can achieve alone. Refactoring is low-risk but limited, replatforming balances effort and reward, and rebuilding is high-stakes with huge potential, with the choice depending on budget, timeline, and how much change an organization can handle.