The question is pretty vague as it stands, but I don’t see how it could be improved in its current state.
Depending on the lifetime, future ownership, and current use of the project you’re maintaining, it may make sense to refactor it as you describe in  and update to the React version you want to use. Yes, it is of course possible, but it is work.
As for , I don’t know either way if it is possible to use different versions of React to render different parts of the project. That would certainly be interesting to see. I would recommend trying to stick to one version across the application — otherwise the next poor soul who needs to update this project will have the same reaction you’ve had.
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