Hello @olivier03
If you change the structure that you are already using in blueprints, it will naturally reset all the values and every blueprint using this structure will need to be re-compiled. Generally I would suggest you avoid changing existing structure. As you can tell, this can cause all sorts of problems. Best to plan ahead or create a new structure altogether. Structures in blueprints can really be a pain at times, it’s a well known fact.
Perhaps using something else, like data assets can better fit your needs. Should also help you with preserving data.