You cannot change the state of an individual component after flattening it. That’s part of the point of flattenStrong; it reduces the number of state changes. You should put that roller under a ModelNode with the appropriate flags set if you want to prevent it from being flattened in with the rest of the conveyor.
If you want to use more than a few hundred objects, you could flatten groups of these objects together (if they don’t have to move independently.) Otherwise, you may consider the RigidBodyCombiner or hardware instancing.