However, I do have a question: how can I use this application to add and change parts from image files? Like png files
Thanks for the question.
If you want to add to the existing ones, there is a folder for parts images in the individual character set folders in the characters folder, so just put the image files in there. Then start CharaMEL. If you want to build your own character sets, the template32x32 folder is a good reference, but the English support is not perfect. This is something we intend to improve in the future.