ok that works:
>>> yv.data = y.clone()
>>> y

 5  5
 5  5
 5  5
[torch.FloatTensor of size 3x2]

>>> yv
Variable containing:
 5  5
 5  5
 5  5
[torch.FloatTensor of size 3x2]

>>> yv.data.fill_(10)

 10  10
 10  10
 10  10
[torch.FloatTensor of size 3x2]

>>> y

 5  5
 5  5
 5  5
[torch.FloatTensor of size 3x2]

>>> yv
Variable containing:
 10  10
 10  10
 10  10
[torch.FloatTensor of size 3x2]