This script bakes the transformation of a node to its offset parent matrix which then acts as its rest matrix. Only works with maya 2020 and up.

bake_to_opm.py

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

TRANSFORM_NODETYPES = ["transform", "joint"]

def has_non_default_locked_attributes(node):
    locked_attributes = []
    for attribute in ["translate", "rotate", "scale", "jointOrient"]:
        default_value = 1 if attribute == "scale" else 0
        for axis in "XYZ":
            if cmds.attributeQuery(attribute + axis, node=node, exists=True):
                attribute_name = "{}.{}{}".format(node, attribute, axis)
                current_value = cmds.getAttr(attribute_name)
                if cmds.getAttr(attribute_name, lock=True) and current_value != default_value:
                    return True


def reset_transforms(node):
    for attribute in ["translate", "rotate", "scale", "jointOrient"]:
        value = 1 if attribute == "scale" else 0
        for axis in "XYZ":
            if cmds.attributeQuery(attribute + axis, node=node, exists=True):
                attribute_name = "{}.{}{}".format(node, attribute, axis)
                if not cmds.getAttr(attribute_name, lock=True):
                    cmds.setAttr(attribute_name, value)


def bake_transform_to_offset_parent_matrix(node):
    if cmds.nodeType(node) not in TRANSFORM_NODETYPES:
        raise ValueError("Node {} is not a transform node".format(node))

    if has_non_default_locked_attributes(node):
        raise RuntimeError("Node {} has at least one non default locked attribute(s)".format(node))

    local_matrix = om.MMatrix(cmds.xform(node, q=True, m=True, ws=False))
    offset_parent_matrix = om.MMatrix(cmds.getAttr(node + ".offsetParentMatrix"))
    baked_matrix = local_matrix * offset_parent_matrix
    cmds.setAttr(node + ".offsetParentMatrix", baked_matrix, type="matrix")

    reset_transforms(node)

def bake_transform_to_offset_parent_matrix_selection():
    for node in cmds.ls(sl=True):
        bake_transform_to_offset_parent_matrix(node)

if __name__ == "__main__":
    bake_transform_to_offset_parent_matrix_selection()

dosent work

// Error: Line 4.21: Syntax error

It's because you try to launch this script as mel. It's python script

Thanks!

Love you man, that script is an absolute banger, saved me hours of copy past