To my knowledge, Swiss property registries work the same way as US/UK ones do, in that they don't create rights, they just record rights that exist. "La constitution, la modification, le transfert et la suppression de ces droits
donnent lieu à une inscription au registre foncier."
https://www.swisstopo.admin.ch/fr/connaissances-faits/cadast...So a property transfer happens, and is then recorded on the registry.
And le "droit d'emption donne à son titulaire
le droit d'acquérir ultérieurement l'immeuble aux conditions fixées dans le contrat." It is "possible," but not mandatory, "de faire annoter ce droit au registre foncier."
https://d-l.ch/fr/articles/le-droit-demptionSo what's being registered is "le droit d'acquérir ultérieurement l'immeuble." The point of registering it is to alert the world that you have the right, so no one can buy the property and then claim they didn't know about your right (first link: "il est exclu de prétendre ignorer une inscription au registre foncier"). If you don't register, a buyer can say they didn't know--then you have to sue the seller for money. If you do register, you can sue the buyer for the property.