hm, ok runtime is a other story. Possible would be creating a small c++ object containing a structure and a method to export as CSV! you can work quite well in excel with a csv.
the next question is how to save it somewhere the excel on the pc get the data from…there are several ways how to connect excel to this external data source.
(Network/Internet=>Database, Lokal Network maybe an CSV/XML on a netshare (XmlParser | Unreal Engine Documentation) …)
if you want to send the entered data back to a api server and save it for example in a mongo db, then i would suggest json.
i think the cleanest and easiest way is: “UE Client → Push data to MySql-DB ← Excel read Data from DB”…but you see - it strongly depends on your requirements and environment, just want to give you some ideas.