How to change default application for apps/portal in 7.9

You can build a plug-in to do that. Notice how I need the application ID which you can get by using this other plug-in "Get Published Applications" (forum.appian.com/.../summary)

Here's an example of the smart service you can create to set the default application

public class DefaultApplicationSetter extends AppianSmartService {          
.....

public defaultApplicationSetter (SmartServiceContext smartServiceCtx,ApplicationService appl) {
super();
this.smartServiceCtx = smartServiceCtx;
this.appl = appl;
}

@Override
public void run() throws SmartServiceException {
appl.setDefaultApplication(appId);
}