MobileNetV2 uses a classifier head with an nn.Dropout layer and the final nn.Linear layer:
model = models.mobilenet_v2()
print(model.classifier)
> Sequential(
  (0): Dropout(p=0.2)
  (1): Linear(in_features=1280, out_features=1000, bias=True)
)

If you want to change the last linear layer, try this code:
model.classifier[1] = nn.Linear(1280, 10)

e.g. to change the number of classes to 10.
model.classifier[1] = nn.Linear(1280, 10)