Well, if you don't mind me asking, what SHOULD I do?
I have not much knowledge about kirbyhats, but just renaming a file almost never works. In a character for example ( i do not know of kirby hats, but may be similar) you open the pac/pcs file and replace the MDL0 with the one you want. Then you do the same with textures and name them correctly. As I said, I have no idea how kirby hats work, but this may give you an idea of what to do.