first you need YY-CHR. the trick is to open two files. one of the sprite you know you want to alter and the other of the graphics you want to use. from there you save another EXGFX.bin file and you copy the graphics in place of the one the sprite originally uses. i know that was very vague but that's how i did it.
by the way my Morton is really Mouser but uses Morton's graphics
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