GUI=Graphical User Interface. It beats having to deal with a console :kikkoman:
I can't really help you with ROM hacking, but I can help you with DS Lazy.
1. Open a ROM by pressing the "..." button
2. Press "NDS Unpack"
3. Wait for it to finish, don't pannic if DS Lazy stops responding, there is a command-line tool in the background, wait for that to finish. the folder "NDS_UNPACK" will pop up.
4. Do whatever you want to do with the data
5. When you're finished, press "NDS PACK", and it will assemble a ROM.
If you need help with ROM hacking, I not your man. I think SCV can help, but I'm not sure.