well i usually do that getting the child of the models in diferent vars, so i can use them independt from the others (remove, add to scene) and to change propierties, i usually destroy em (remove from scene, setting them nulls,etc...) and put them back in scene with new properties, dont try to remove from scene and adding new one, cause i think it cause some memory leak, at least in olders versions.
hope this helps.
