My recommendation for you is to use mkksiso instead to add your kickstart. That command also lets you add your own kernel options if you so wish using -c. And then you can write the ISO to the USB using one of the recommended tools.
If you insist on making changes manually, there are specific steps you have to take to rebuild it for it to work properly. You should not be changing the label for stage2 unless you’ve generated your very own stage2 image (which requires knowledge of lorax). I would look at this post to see how we make our initial images. It’s a very specific process, and thus it is why I recommend that you use mkksiso.