Thanks @mogoodrich for reminding us about the kind of approach that you guys follow.
@aniket, so what can be done for sure is to add your own extension through your custom module, the same way the Registration App module does it (see my last post). And then, to make sure that your custom extension is being picked up, you could disable the “default” one (=the one defined by the Reg. App module) through your custom module’s activator. With something like that:
AppFrameworkService service = Context.getService(AppFrameworkService.class);
service.disableExtension("org.openmrs.module.registrationapp.editPatientDemographics");
The id of the extension point "org.openmrs.module.registrationapp.editPatientDemographics" was inferred from this line.