In my understanding, this code would work. I have not test it, but it is something worth trying.
optim.SGD([
        {'params': other_parameters}
        {'params': model.conv_layer.weight, 'lr': 1e-3, 'weight_decay': 0.9},
        {'params': model.conv_layer.bias, 'lr': 1e-3, 'weight_decay': 0.0}
    ], lr=1e-2, momentum=0.9, weight_decay=0.98)