There are a few ways to go about only loading deltas. If you can track this in your data source (MySQL, SAP, etc), it offloads the burden to your database. If not, you can do a full load into a data hub, where locking the model during an import isn't consequential because users wouldn't be performing any work in that model - from there it's easy to perform a calculation to look for changes from the previous load. Create a boolean line item that is true when there are changes, and a saved view based on that from which you import into your spoke model(s).
Jesse Wilson Solution Architect - Data Integrations Singapore