Error 327426 means that the Program is already installed. In cases like this, you can simply add this code to your Success Codes field. This way when a deployment is attempted and the program is already installed it won't return as a failed deployment.
Error 327424 seems to be similar to the standard success code of 3010. This code simply means "Successful installation and a reboot is required". I'm not sure why Microsoft didn't just have this return 3010 but there you go. I haven't found definitive documentation from Microsoft about this error but I have seen many references online stating that it simply means a reboot is needed.