Is it possible to create local material overrides on rendering properties at the object level, as one can do with shader parameters?
The only way to achieve that seems to be to redefine the properties again, but that is quite slow and disrupts the niceties with materials…Is there a workaround , or it is not possible at all?

at the OBJ level, there is a Material tab on your object. The far right button is an arrow pointing down. Click on it and it gives you the option to Create Local Material Parameters. Changes will only affect that object.

Any materials and shaders inside the object will not be overridden.

is that what you were looking for?

No, as I said material shader parameter overrides are working fine, my question was about rendering properties (RMan attributes), which are not altered.

diula
No, as I said material shader parameter overrides are working fine, my question was about rendering properties (RMan attributes), which are not altered.

This is currently a bug with material overrides.

However, the work-around (at the object level at least), is to simply add the property you would like to override.

If the parameter exists on the object itself, it has precedence over the material property.