Again something I havent tried BUT the reactive angular calls the tags/selectors SO in your extension import your new record container class, then in your extension.module.ts try and declare the new container so try this:
import {RecordModalComponent} from "./components/modal/record-modal/record-modal.component";
...
@NgModule({
declarations: [RecordModalComponent],
imports: [
obviously RecordModalComponent should be replaced by your new RecordContainer class.