https://usagi.hatenablog.jp/entry/2020/04/13/230904

blender-merge-vertex-groups.py

import bpy
from re import compile

print('')

# Target(s) REGEX
regex = compile( '^Edit(KamiARoot|MaeKamiA(_00[1,2])?)$' )
# Replace Mode := Remove a target(s) -> new a merged
replace = True
# Merged name; "+".join if None
to = 'EditKamiARoot'
# Dry run
dry = True

ob = bpy.context.active_object

group_lookup = {g.index: g.name for g in ob.vertex_groups}
group_candidates = {n for n in group_lookup.values() if regex.match(n)}

# test whether all candidates components of group_lookup
if all(n in group_lookup.values() for n in group_candidates):
    pass

# general tests
if (len(group_candidates) and ob.type == 'MESH' and
    bpy.context.mode == 'OBJECT'):
    
    # iterate through the vertices and sum the weights per group
    vertex_weights = {}
    for vert in ob.data.vertices:
        if len(vert.groups):  
            for item in vert.groups:
                vg = ob.vertex_groups[item.group]
                if vg.name in group_candidates:
                    if vert.index in vertex_weights:    
                        vertex_weights[vert.index] += vg.weight(vert.index)
                    else:
                        vertex_weights[vert.index] = vg.weight(vert.index)
        
    # clamp/slice values above 1.0
    for key in vertex_weights.keys():
        if (vertex_weights[key] > 1.0): vertex_weights[key] = 1.0
    
    # remove sources
    if replace:
        for g in group_candidates:
            if dry:
                print('be remove(dry-run): ', g)
            else:
                ob.vertex_groups.remove(ob.vertex_groups.get(g))
                print('removed:', g)
    
    # create new vertex group
    new_name = to if to != None else "+".join(group_candidates)
    if dry:
        print('be merge(dry-run):', new_name)
    else:
        vgroup = ob.vertex_groups.new(name=new_name)
        print('merged: ', vgroup.name)
        
        # add the values to the group                       
        for key, value in vertex_weights.items():
            vgroup.add([key], value ,'REPLACE') #'ADD','SUBTRACT'