For debris, you'll need to modify one of the radio_*.bnk files in [GP4 Folder]\Samples, where '*' is a 3-letter language abbreviation.
Lo2K's
Sample Editor will allow you to edit the .bnk files (they're just like archives) and replace the correct file once you work out which one it is.
You might also need to convert your sounds to the correct format, but I don't much about that.
I don't think sounds for flags are possible though.
F1 Graphics Swapper ---
Lensdump - Renders and Screenshots ---
GP4 Performance Generator