I am also stuck on this. Looking at the code of _init_weights, it looks like it expects individual modules like nn.Linear.
This would require looping over all the modules of your model that you would like to re-initialize and passing them to _init_weights. But this might not translate to a new model, as their layer structure could be different. Is there not a way to just re-initialize a whole layer? Or all modules under some component (e.g. BertLayer)?