I've seen some models where there's an option to smooth on render.
There was even a script to smooth the object.
Special thing here was you could uncheck things in the attribute editor to go back to the lowpoly object.

I know you can smooth an object, but that's permanent. No?
And hitting 3 give a preview of the smoothing.
But that's not what I've seen.

Any ideas how to set this up?
Thx!