I'm sorry for my bad English. I am really incompetent in advance Gimp using.
I would like to modify the "down right corner" symbol of 'Note_Cymbal_Yellow_Sizzle.png' in order to look like the 'Note_Cymbal_Miss_Sizzle.png' symbol but I don't know how to do that. I would copy/paste the "down right corner" symbol in the other file to obtain the 3 other corners.
I imagine it's a basic manipulation for an expert.