Thanks a lot @ptrblck for your support.
Please see the issue below.
Code:
FILE = "fmnist_scripted.pt"
scripted_model = torch.jit.load(FILE)

for i in scripted_model.named_modules():
    print (i)

myfc3 = nn.Linear(in_features=120, out_features=10)
scripted_fc3 = torch.jit.script(myfc3)
scripted_model.fc3 = scripted_fc3

Output:
('', RecursiveScriptModule(
  original_name=FashionCNN
  (layer1): RecursiveScriptModule(
    original_name=Sequential
    (0): RecursiveScriptModule(original_name=Conv2d)
    (1): RecursiveScriptModule(original_name=BatchNorm2d)
    (2): RecursiveScriptModule(original_name=ReLU)
    (3): RecursiveScriptModule(original_name=MaxPool2d)
  )
  (layer2): RecursiveScriptModule(
    original_name=Sequential
    (0): RecursiveScriptModule(original_name=Conv2d)
    (1): RecursiveScriptModule(original_name=BatchNorm2d)
    (2): RecursiveScriptModule(original_name=ReLU)
    (3): RecursiveScriptModule(original_name=MaxPool2d)
  )
  (fc1): RecursiveScriptModule(original_name=Linear)
  (drop): RecursiveScriptModule(original_name=Dropout2d)
  (fc2): RecursiveScriptModule(original_name=Linear)
  (fc3): RecursiveScriptModule(original_name=Linear)
))
('layer1', RecursiveScriptModule(
  original_name=Sequential
  (0): RecursiveScriptModule(original_name=Conv2d)
  (1): RecursiveScriptModule(original_name=BatchNorm2d)
  (2): RecursiveScriptModule(original_name=ReLU)
  (3): RecursiveScriptModule(original_name=MaxPool2d)
))
('layer1.0', RecursiveScriptModule(original_name=Conv2d))
('layer1.1', RecursiveScriptModule(original_name=BatchNorm2d))
('layer1.2', RecursiveScriptModule(original_name=ReLU))
('layer1.3', RecursiveScriptModule(original_name=MaxPool2d))
('layer2', RecursiveScriptModule(
  original_name=Sequential
  (0): RecursiveScriptModule(original_name=Conv2d)
  (1): RecursiveScriptModule(original_name=BatchNorm2d)
  (2): RecursiveScriptModule(original_name=ReLU)
  (3): RecursiveScriptModule(original_name=MaxPool2d)
))
('layer2.0', RecursiveScriptModule(original_name=Conv2d))
('layer2.1', RecursiveScriptModule(original_name=BatchNorm2d))
('layer2.2', RecursiveScriptModule(original_name=ReLU))
('layer2.3', RecursiveScriptModule(original_name=MaxPool2d))
('fc1', RecursiveScriptModule(original_name=Linear))
('drop', RecursiveScriptModule(original_name=Dropout2d))
('fc2', RecursiveScriptModule(original_name=Linear))
('fc3', RecursiveScriptModule(original_name=Linear))

---------------------------------------------------------------------------
RuntimeError                              Traceback (most recent call last)
<ipython-input-31-3c19b7b057b1> in <module>
     13 myfc3 = nn.Linear(in_features=120, out_features=10)
     14 scripted_fc3 = torch.jit.script(myfc3)
---> 15 scripted_model.fc3 = scripted_fc3
     16 #############################################################################################
     17 # Carving out & saving layers one-by-one

~/pyvenv/lib/python3.6/site-packages/torch/jit/_script.py in __setattr__(self, attr, value)
    672 
    673             if attr in self._modules:
--> 674                 self._modules[attr] = value
    675             elif self._c.hasattr(attr):
    676                 self._c.setattr(attr, value)

~/pyvenv/lib/python3.6/site-packages/torch/jit/_script.py in __setitem__(self, k, v)
    221         # otherwise it's illegal and we throw error.
    222         if isinstance(v, ScriptModule):
--> 223             self._c.setattr(k, v)
    224             self._python_modules[k] = v
    225         else:

RuntimeError: Expected a value of type '__torch__.torch.nn.modules.linear.___torch_mangle_4.Linear (of Python compilation unit at: 0x10687bf0)' for field 'fc3', but found '__torch__.torch.nn.modules.linear.___torch_mangle_4.Linear (of Python compilation unit at: 0x3965610)'