Yes, Scene Fusion is fussy about code changes. It cares about seralizeable properties - the name, order, and value of them. You can get away with logic modifications, and adding new code, however modifying existing code, specifically the public/serializable data, will cause Scene Fusion to say "uh, wait a minute...". The reason is because it treats everything like a collection of properties - effectively a multi-type key/value pair store, so if one person has a different set of values for a given component, then the method of syncing changes for those values becomes undefined. We have some ideas in the works that might be workable as a solution to this problem.
Other assets can be modified and distributed while Scene Fusion is running. If you create a new asset, you can even start placing it in the scene, and your other collaborators will see a red "?" where the asset should be. Once you check it in and they pull in the change, everything gets updated automatically in their scene.
We have a discord server running. Feel free to pop in and chat if you have questions: https://discord.gg/z6xBcvq