つかいかた: アーマチュアを選択した状態で、nキーを押すと出てくるメニューのtoolにあるApply Subbonesボタンを押すだけ (https://twitter.com/totegamma/status/1574051804765376512/photo/1)

apply_subbones.py

import bpy
import re
import sys

bl_info = {
    "name" : "Apply Subbones",
    "author" : "totegamma",
    "version" : (0, 1, 0),
    "blender" : (3, 3, 0),
    "description" : "Apply Subbone weights and cleanup them.",
    "category" : "Rigging"
}

class APPLYSUBBONES_OT_Main(bpy.types.Operator):
    bl_idname="applysubbones.main"
    bl_label="Apply Subbones"
    bl_options = {'REGISTER', 'UNDO'}

    @staticmethod
    def ShowMessageBox(message = "", title = "Message Box", icon = 'INFO'):
        def draw(self, context):
            self.layout.label(text=message)
        bpy.context.window_manager.popup_menu(draw, title = title, icon = icon)

    @staticmethod
    def findProperBone(bone):
        itr = bone
        while True:
            if re.match(bpy.context.scene.subbone_filter, itr.parent.name):
                itr = itr.parent
            else:
                return itr.parent

    @staticmethod
    def createModifiers():
        target = bpy.context.active_object

        if (target.type != "ARMATURE"):
            ShowMessageBox("please select armature", "error", 'ERROR')
            return

        bones = target.data.bones
        subbones = list(filter(lambda x: re.match(bpy.context.scene.subbone_filter, x.name), bones))
        print(list(map(lambda x: f"{x.name} -> {x.parent.name}", subbones)))

        targetmeshes = list(filter(lambda x: x.type == 'MESH', target.children))
        print(targetmeshes)

        for mesh in targetmeshes:
            for bone in subbones:
                parent = APPLYSUBBONES_OT_Main.findProperBone(bone)
                print(f'add {bone} to {mesh}')
                if not ((bone.name in mesh.vertex_groups) and (parent.name in mesh.vertex_groups)):
                    continue
                mod = mesh.modifiers.new(f"ApplySubBoneWeight: {bone.name} to {parent.name}", "VERTEX_WEIGHT_MIX")
                mod.vertex_group_a = parent.name
                mod.vertex_group_b = bone.name
                mod.mix_set = 'ALL'
                mod.mix_mode = 'ADD'
                mod.show_expanded = False

    @staticmethod
    def applyAndCleanup():
        target = bpy.context.active_object
        if (target.type != "ARMATURE"):
            ShowMessageBox("please select armature", "error", 'ERROR')
            return

        bones = target.data.bones
        subbones = list(filter(lambda x: re.match(bpy.context.scene.subbone_filter, x.name), bones))
        targetmeshes = list(filter(lambda x: x.type == 'MESH', target.children))

        for mesh in targetmeshes:
            bpy.ops.object.select_all(action='DESELECT')
            if not mesh.name in bpy.context.view_layer.objects:
                continue
            bpy.context.view_layer.objects.active = mesh

            for mod in list(filter(lambda x: x.type == 'VERTEX_WEIGHT_MIX', mesh.modifiers)):
                bpy.ops.object.modifier_apply(modifier=mod.name)

            for vg in list(map(lambda x: x.name, subbones)):
                if vg in mesh.vertex_groups:
                    bpy.ops.object.vertex_group_set_active(group=vg)
                    bpy.ops.object.vertex_group_remove()

        bpy.ops.object.select_all(action='DESELECT')
        bpy.context.view_layer.objects.active = target

        bpy.ops.object.mode_set(mode='EDIT')
        subbones = list(filter(lambda x: re.match(bpy.context.scene.subbone_filter, x.name), target.data.edit_bones))
        for bone in subbones:
            target.data.edit_bones.remove(bone)
        bpy.ops.object.mode_set(mode='OBJECT')

    def execute(self, context):
        self.createModifiers()
        self.applyAndCleanup()
        self.ShowMessageBox("complete!", "message")
        return {'FINISHED'}

class APPLYSUBBONES_PT_Toolpane(bpy.types.Panel):
    bl_idname = "object.custom_panel"
    bl_label = "Apply Subbones"
    bl_space_type = "VIEW_3D"   
    bl_region_type = "UI"
    bl_category = "Tool"
    bl_context = "objectmode"

    def draw(self, context):
        layout = self.layout
        layout.prop(bpy.context.scene, "subbone_filter")
        layout.operator(APPLYSUBBONES_OT_Main.bl_idname, text = "Apply Subbones")



def register():
    bpy.types.Scene.subbone_filter = bpy.props.StringProperty(
        name = "filter Regex",
        description = "regex for filtering subbones",
        default = ".*\.[0-9]+$"
    )

    bpy.utils.register_class(APPLYSUBBONES_OT_Main)
    bpy.utils.register_class(APPLYSUBBONES_PT_Toolpane)

def unregister():
    bpy.utils.unregister_class(APPLYSUBBONES_OT_Main)
    bpy.utils.unregister_class(APPLYSUBBONES_PT_Toolpane)

if __name__ == "__main__":
    register()