In the end I didn’t need to unwind the segue since I could still get a reference to the parent controller methods by following the navigation controller.
I was able to get a reference by doing the following in the - (void)viewWillDisappear:(BOOL)animated method of the child controller
NSInteger currentVCIndex = [self.navigationController.viewControllers indexOfObject:self.navigationController.topViewController];
FirstViewController *parent = (FirstViewController *)[self.navigationController.viewControllers objectAtIndex:currentVCIndex];
parent.barcodeType = indexPath.row;
which passed the settings variable back to the original controller perfectly.
I also added an import reference to the parent controller at the top of the childcontroller