Directly Apply Delta Blendshape

You cant directly sculpt on the blendshape since it has a different space. So normally I duplicate the model and sculpt in its static state.

After which, I applied the static to the blendshape pose. This will generate the delta pose in the background.

The script to apply

import pymel.core as pm

def go():
    target = pm.ls('target')[0] # driven    
    source = pm.ls('source')[0] # driver
    for vtx in source.vtx:
        idx = vtx.index()
        t = pm.xform(vtx, q=True, t=True)

        output = target.vtx[idx]
        pm.move(output, t, a=True)
        
go()

# Version with using it on a specified points
import maya.cmds as cmds
import pymel.core as pm


# Get the selection from the set named 'point_selection'
selected_points = cmds.sets('point_selection', q=True)

def flatten_list(selected_objects): # selected objects is a vertex list
    # Check if there are any objects in the selection
    vertex_list = []
    if selected_objects:
        for obj in selected_objects:
            if cmds.objectType(obj) == 'mesh':  # Check if the object is a mesh
                # Extracting the number range from the vertex string
                vertex_range = obj.split('[')[-1].split(':')
                start_index = int(vertex_range[0])
                end_index = int(vertex_range[-1].rstrip(']'))

                # Constructing individual vertex names
                for i in range(start_index, end_index + 1):
                    vertex_list.append(f"{obj.split('.')[0]}.vtx[{i}]")

    else:
        vertex_list = []
    
    return vertex_list        


def transfer_points(selected_points=None):
    source = pm.ls('source_geo')[0]
    target = pm.ls('target_geo')[0]

    if selected_points:
        vertex_list = selected_points
    else:
        vertex_list = source.vtx

    for vtx in vertex_list:
        
        vtx = pm.PyNode(vtx)
        idx = vtx.index()
        t = pm.xform(vtx, q=True, t=True)

        output = target.vtx[idx]
        pm.move(output, t, a=True)
        
processed_points = flatten_list(selected_points)
transfer_points(selected_points=processed_points)