Hi Maria,

There is no equivalent in the ZPL but you can use the ZOS-API to accomplish this.  You can use the built-in function from the Lens Catalog tool under the Libraries tab (TheSystem.Tools.OpenLensCatalogs()), but this will only allow you to insert a lens from a ZMF vendor catalog.  If you want insert a custom ZMX/ZOS file, you can create 2 IOpticalSystem using the same connection and then use TheSystem.LDE.CopySurfacesFrom() to copy the surfaces from one optical system to the other.  Below is Python code to achieve this second suggestion: 

import zosapi, os

# connect to OpticStudio

zos = zosapi.App()

# create a second system

zos.TheSystem2 = zos.TheApplication.CreateNewSystem(zos.ZOSAPI.SystemType.Sequential);

# load the files: TheSystem will be the main file and TheSystem2 will be the file you want to insert

zos.TheSystem.LoadFile(os.path.join(zos.TheApplication.SamplesDir, r'Sequential\Objectives\Double Gauss 28 degree field.zmx'), False)

zos.TheSystem2.LoadFile(os.path.join(zos.TheApplication.SamplesDir, r'Sequential\Objectives\Doublet.zmx'), False)

# copy the surfaces into the main system

zos.TheSystem.LDE.CopySurfacesFrom(zos.TheSystem2.LDE, 1, zos.TheSystem2.LDE.NumberOfSurfaces - 2, 1)

# save system & verify

zos.TheSystem.SaveAs(os.path.join(zos.TheApplication.ZemaxDataDir, 'insertlens.zmx'))

Thank you, Michael!