Hi, I took the liberty to update the "io_phxbn" plugin from the blender addon distributed in the game files to be usable for newer versions of Blender (2.92 and above). This way you can do your modeling in a more convenient and modern way

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I put it in a github repo here :
https://github.com/RougailSaucisse/io_phxbn . Download, put in a zip and add to Blender.
Don't forget the wiki's tutorial here :
https://wiki.wolfire.com/index.php/Custom_Characters
Have fun !