Maybe this will help someone…
When you switch a component instance into another one, sometimes Figma will fail to identify the similarities, and it will prevent it from keeping your data. It is frustrating to see all your customizations reset to the component defaults. This is especially true if the old and the new component are compex and/or different in structure.
It definitely helps if you call your internal objects (e.g. texts, rectangles, frames etc.) by the same name in the old and new component. However, sometimes that even is not enough hint for Figma to carry over your customizations to the new object.
In these cases it seems to help if you create an interim component with an internal structure that is in between that of the OLD and NEW component.
Enjoy,
K