1.) This obviously depends on the specific game.

2.) Short answer: No. Long answer: Nope.

Well, the long answer for 2 is "Yes" but it's a yes that will take years of hard work and practice to make.

You might want to check the pokecommunity tutorial forum for scripting help.

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This.

Man, if putting in any music in any game was that easy no matter the medium it was on, that alone would make the world of romhacking tons better in my eyes.  :happy:  Can you imagine all the people that hacked Super Mario Bros 1 if they were able to use remixed music made with real instruments or an orchestrated arrangement of a song in the game? That would kick so much ass.    Especially for people who love official remixes of game music.

Changing the existing music on a CD based system where the music streams off the disc is probably the easiest place I think were you can change the music if you know what to do. But to add a radio feature where you can tune into songs whenever you want is a whole other world. Even if you could add such a feature, don't expect to play real music on a console that can only handle chiptuned music. It would be so awesome if you could though.