You can just modify the parameters. In torch 0.4 or master, you’d do:
import torch
l = torch.nn.Linear(2,3)
l2 = torch.nn.Linear(2,3)
with torch.no_grad():
    l2.weight.copy_(torch.sign(l.weight))
print(l.weight, l2.weight)

in torch 0.3, you operate on weight.data instead of weight directly, but can do it the same way otherwise.
You can also use your favourite way of accessing parameters (e.g. model.parameters(), model.named_parameters(), model.state_dict()) instead of explicitly coding them.
Best regards
Thomas