Is it possible to resize a buffer after it has been declared?

Yes, you can do .resize_(). Note that the content of the Tensor will be un-initialized though. So you need to make sure that you either zero it or write some value before using it.

And additionally is it possible to add a buffer after DataParallel has been called?

Maybe but I would not recommend that. It sounds quite fragile.

if I have 10 buffers do I need to have them all have a personal name or can I make an array of buffers?

No you cannot do an array of buffers at the moment. You will have to register them one by one.