Export each single entity customization and keep each entity customization in a separate file, like:
This way, if an entity is changed or broken on the Live environment, you can re-import the customization for this entity again, without breaking other entities on live environment.
Instead of exporting each single entity, you can also export only your customized entities in 1 step, and afterwards select what entities to import
Figure: You can select the single customization to import