The Service Builder allows you to redefine both OData services created in SAP Gateway and external services (SPI, BW Query, GenIL) that have been created using different backend frameworks.
See Redefining OData Service (SAP GW) to redefine OData services created in SAP Gateway.
See Redefining Services from External Framework (SPI, BW Query, GenI for redefining services of different frameworks.