Here is a script

 

find node attached to diffuse and disconnect

add image map x 2

add blender node

connect all

import poser, string

image files

myimg = ":Runtime:Textures:myimgs:myimg.jpg"
mymask = ":Runtime:Textures:myimgs:mymask.jpg"

fig = poser.Scene().CurrentFigure()
mat = fig.Material("2_SkinTorso")

nod = mat.ShaderTree().NodeByInternalName("PoserSurface")
inp = nod.InputByInternalName("Diffuse_Color")
mynode = inp.InNode()
if mynode:
    inp.Disconnect()

create nodes

blend

blndnode = mat.ShaderTree().CreateNode(poser.kNodeTypeCodeBLENDER)
blndnode.SetName("Overlay Blender")
blndnode.SetPreviewCollapsed(0)
blndnode.SetInputsCollapsed(1)
blndnode.SetLocation(231,80)
inpdif = blndnode.Input(0)
inpimg = blndnode.Input(1)
inpmask = blndnode.Input(2)
blndnode.Input(2).SetFloat(1)

overlay image

imgnode = mat.ShaderTree().CreateNode(poser.kNodeTypeCodeIMAGEMAP)
imgnode.SetName("Overlay Image")
imgnode.SetPreviewCollapsed(0)
imgnode.SetInputsCollapsed(1)
imgnode.SetLocation(231,111)
#imgnode.Input(0).SetString(myimg) # remove comment to enable <<<<<<<<<<<<<

overlay mask

masknode = mat.ShaderTree().CreateNode(poser.kNodeTypeCodeIMAGEMAP)
masknode.SetName("Overlay Mask")
masknode.SetPreviewCollapsed(0)
masknode.SetInputsCollapsed(1)
masknode.SetLocation(231,141)
#masknode.Input(0).SetString(mymask) # remove comment to enable <<<<<<<<<<<<<

connect

mynode.ConnectToInput(inpdif)   # connect diffuse map original to blender
imgnode.ConnectToInput(inpimg)  # connect overlay map  to blender
masknode.ConnectToInput(inpmask) # connect mask to blender
blndnode.ConnectToInput(inp)     # connect blender to diffuse

update preview and redraw scene

mat.ShaderTree().UpdatePreview()
poser.Scene().DrawAll()

 

it finds and detaches the node plugged into Diffuse color

creates a blender and two image nodes

myimg is the overlay image

mymask is the overlay mask

plugs the node from the diffuse color into blender

plugs the blender node into diffuse color

 

this may not be all thats needed but should be close

I may have to unplug and attach blender to specular as well  ?

This is hardcoded to overlay onto 2_SkinTorso material  , that is what I need to know or I can make it current selected material .

the script needs some changes , uncomment the two lines that set the image names , and edit the script to use the proper image names rather than my test names

rename it to a .py extension and put in the poser python folder. run from file menu.