PyTorch uses the internal _register_state_dict_hook and _register_load_state_dict_pre_hook. However, since these methods are internal their interface could change without a deprecation warning, so I wouldn’t depend on them.
Based on your description it seems you are looking for a “post_state_dict_hook”?
If so, wouldn’t applying the desired manipulations to the model parameters after calling model.load_state_dict work? I’m unsure why a hook would be needed for it.