Override UnityAppController in iOS

I want to pass a parameter to an Unity iOS app via a URL using an iOS plugin. I have successfully passed a parameter via URL by adding/editing the following the UnityAppController in Xcode:

 - (void) callUnitySendMessage:(const char*)object Method:(const char*)method Parameter:(const char*)parameter
 {
     UnitySendMessage(object, method, parameter);
 }
 
 - (BOOL)application:(UIApplication*)application openURL:(NSURL*)url sourceApplication:(NSString*)sourceApplication annotation:(id)annotation
 {
 
   NSString* hostString = url.host;
     
     [self callUnitySendMessage:"NativeInterfaceReceiver"
                    Method:"TestThisFunction"
                 Parameter:hostString.UTF8String];
 
     NSMutableArray* keys    = [NSMutableArray arrayWithCapacity:3];
     NSMutableArray* values    = [NSMutableArray arrayWithCapacity:3];
 
     #define ADD_ITEM(item)    do{ if(item) {[keys addObject:@#item]; [values addObject:item];} }while(0)
 
     ADD_ITEM(url);
     ADD_ITEM(sourceApplication);
     ADD_ITEM(annotation);
 
     #undef ADD_ITEM
 
     NSDictionary* notifData = [NSDictionary dictionaryWithObjects:values forKeys:keys];
     AppController_SendNotificationWithArg(kUnityOnOpenURL, notifData);
     return YES;
 }

I’d prefer to do this via a Unity plugin so that I don’t have to edit anything in Xcode. I figure I should be able to do this by overriding this function with a subclass of UnityAppController called MyAppController under Plugins/iOS. But how do I get MyAppController to replace UnityAppController? This is what I have so far--not sure if I'm on the right track.