Create a pre bind matrix joint for skincluster for selected joints to tweak the pre bind matrix easily

maya_joints_recreate_prebindmatrix.py

import re
from maya import cmds
import maya.api.OpenMaya as om

def nodename(n):
    return n.rsplit("|", 1)[-1].rsplit(":", 1)[-1]


for joint in cmds.ls(type="joint", sl=True):
    jointname = nodename(joint)
    
    destinations = cmds.listConnections(joint + ".worldMatrix", source=False, destination=True, plugs=True, type="skinCluster") or []
    for destination in destinations:
        skin, attr = destination.split(".", 1)
        match = re.search(r"^matrix\[(\d+)\]$", attr)
        if not match:
            continue
            
        index = int(match.group(1))
        
        # Get the bindPreMatrix for that influence index
        bind_prematrix_plug = f"{skin}.bindPreMatrix[{index}]"
        bind_prematrix = cmds.getAttr(bind_prematrix_plug)
        
        if bind_prematrix is None:
            # Can happen if the value is not initialiezd - if so
            # assume the current joints position
            bind_prematrix = cmds.xform(joint, query=True, worldSpace=True, matrix=True)
            bind_prematrix = om.MMatrix(bind_prematrix).inverse()
            
        bind_prematrix_inv = om.MMatrix(bind_prematrix).inverse()
        bind_prematrix_inv = list(bind_prematrix_inv)
        
        # Create matching prebind joint as input
        bind_prematrix_joint = cmds.createNode("joint", name=f"{jointname}_bindPreMatrix_for_{skin}")
        cmds.xform(bind_prematrix_joint, worldSpace=True, matrix=bind_prematrix_inv)
        cmds.connectAttr(bind_prematrix_joint + ".worldInverseMatrix[0]", bind_prematrix_plug)
    

Deleting or disconnecting the bindPreMatrix joints that are created will clear the bindPreMatrix value instead of persisting them for the skincluster. As such, we'll need to disconnect and set the value explicitly. Here's a trivial way to do so after using the script above:

from maya import cmds

def pairwise(iterable):
    it = iter(iterable)
    return zip(it, it)


for skin in cmds.ls(type="skinCluster"):
    connections = cmds.listConnections(skin + ".bindPreMatrix", source=True, destination=False, connections=True, plugs=True) or []
    for dest, src in pairwise(connections):
        value = cmds.getAttr(dest)
        cmds.disconnectAttr(src, dest)
        cmds.setAttr(dest, value, type="matrix")