How to use Reforged models that also work in classic?

[nvhazard]

How to make Reforged only models to be backed up by models in Classic?

For example orc skeletons have their own models in Reforged and only one model in Classic. But when I make a custom unit and set their model to Reforged orc skeleton then it does not shows in classic?

I think there was a trigger that changes skin/model for a unit, can I manually check if player is on classic and change the model?

Would be nice if there was a parameter in object editor for classic models, but I did not found it.