This will swap all Specular BSDf nodes to Principled BSDF nodes. However there the specular color parameter isn't available on the Principled BSDf so you may experience loss of data there.

import bpy

for mat in bpy.data.materials:
    if not mat.use_nodes:
        continue
    nodes = mat.node_tree.nodes
    specular = next((n for n in nodes if isinstance(n, bpy.types.ShaderNodeEeveeSpecular)), None)
    output = next((n for n in nodes if isinstance(n, bpy.types.ShaderNodeOutputMaterial)), None)
    if specular is None or output is None:
        continue
    principled = nodes.new("ShaderNodeBsdfPrincipled")
    principled.inputs[0].default_value = specular.inputs[0].default_value  # Color
    principled.inputs[9].default_value = specular.inputs[2].default_value  # Roughness
    principled.inputs[19].default_value = specular.inputs[3].default_value  # Emission color
    principled.inputs[21].default_value = 1 - specular.inputs[4].default_value  # Alpha
    principled.inputs[14].default_value = specular.inputs[6].default_value  # Clearcoat
    principled.inputs[15].default_value = specular.inputs[7].default_value  # Clearcoat roughness
    
    principled.location = (specular.location[0] - 100, specular.location[1])    
    mat.node_tree.links.new(principled.outputs[0], output.inputs[0])
    nodes.remove(specular)

This will swap all Specular BSDf nodes to Principled BSDF nodes. However the specular color parameter isn't available on the Principled BSDF so you may experience loss of data there.

import bpy

for mat in bpy.data.materials:
    if not mat.use_nodes:
        continue
    nodes = mat.node_tree.nodes
    specular = next((n for n in nodes if isinstance(n, bpy.types.ShaderNodeEeveeSpecular)), None)
    output = next((n for n in nodes if isinstance(n, bpy.types.ShaderNodeOutputMaterial)), None)
    if specular is None or output is None:
        continue
    principled = nodes.new("ShaderNodeBsdfPrincipled")
    principled.inputs[0].default_value = specular.inputs[0].default_value  # Color
    principled.inputs[9].default_value = specular.inputs[2].default_value  # Roughness
    principled.inputs[19].default_value = specular.inputs[3].default_value  # Emission color
    principled.inputs[21].default_value = 1 - specular.inputs[4].default_value  # Alpha
    principled.inputs[14].default_value = specular.inputs[6].default_value  # Clearcoat
    principled.inputs[15].default_value = specular.inputs[7].default_value  # Clearcoat roughness
    
    principled.location = (specular.location[0] - 100, specular.location[1])    
    mat.node_tree.links.new(principled.outputs[0], output.inputs[0])
    nodes.remove(specular)