If I create a callback like this:
callbacks.addScript #prerender "teapot()" id:#teapot
and then hit render with DR on (VRay) the teapot is created AFTER the scene is sent to slaves so this computer renders the scene with teapot and the slaves render it without.
Now I’d like to know is there any way of getting the teapot in BEFORE the scene is sent to the slaves?
to have scripts run on the renderfarm you could make the callback #persistent. but since it will be evaluated on every machine, you might have inconsistencies. at least the color of the teapot in your example…
as for your initial idea to create your teapot like #preNetSend i didn´t find anything to attach the callback to. so maybe try specifying the stuff exactly (e.g. color of teapot) so that it will be created the same on every machine in the farm.