It returns
{'params': [Parameter containing:
tensor([[ 0.0788, -0.3615,  0.4415,  0.2667, -0.3098],
        [-0.3995,  0.0706,  0.4255, -0.3650,  0.3453]], requires_grad=True), Parameter containing:
tensor([ 0.1224, -0.2431], requires_grad=True)], 'lr': 0.001, 'momentum': 0.9, 'dampening': 0, 'weight_decay': 0, 'nesterov': False}

Here is the full code:

import torch
import torch.optim as optim

model = torch.nn.Linear(5, 2)

# Initialize optimizer
optimizer = optim.SGD(model.parameters(), lr=0.001, momentum=0.9)
new = torch.randn(5, 5)
print(new)
optimizer.param_groups.append({'params': new})

print("---")
print(optimizer.param_groups[0])

I would like to see new tensor weights somehow in the optimizer.