Hi @Martin_Mundt,
We are also doing continual learning. And we have been following the method as you have suggested at the end, i.e., redefining the Layer and assigning the weights values according to the old weights and the initialization for the new slice. So far, it has worked for us, through pytorch 0.4 to 1.1.
Commenting here so that we can see if there is better way to do this than the method described above.