Updating table without losing previous rows

It is not possible in Power BI Desktop RS standaone. If you need incrementally add data to model, you need use dedicated PBI model hosted on SSAS instance (with live connection to PBI report). It allows incrementally adding data and parition processing options.

But moreover, independly if use PBI Desktop model or SSAS dedicated model, in this case I recommends use another data layer (like MSSQL DB, or any no-sql store) to persis data history, and PBI/SSAS model use only as analytic/reporting layer. PBI/SSAS prvide great query performance due to inmemory collumn store, but are not great as persisted row store.