I honestly don't know the ins and outs of this. If you want to use other wings than the 27 available in 1.69, you probably at least have to add the models to your wingmodel.2da and include it and the model files into HAKs used by the module.
If the issue is just whether Leto supports wing models that aren't in its help list, I am pretty sure it does, though it only shows the entries from the 1.69 wingmodel.2da file. But, you should be able to enter any value that's valid in the 2DA using Leto. For example, CEP 2.4 has a huge list of wings (many of which are cool FX that show up at a character's wing location). I can use Leto to change the Wings_New entry to 687 which isn't in it's help list, but which corresponds to the "@VFX: Tendrils, Holy" entry in CEP's wingmodel.2da (from cep2_top_v24.hak). That makes the weird tendril effect replace the wings on my test red dragon disciple character when I load her into a CEP 2.4 module.
People in the
Custom Content forum would probably have better information.
