Yes, you can!
At first, open up the part from the imported assembly.
Then use SWX features to add fillets, cuts, bores or add material.
If you want to change the dimension then please try direct editing feature like "move face".
With the feature "delete face" you should be able to delete some geometry.
You also may try "FeatureWorks" to make a sketch/feature recognition to get a parametric part. Then you'll be able to make changes as you are used to like in any other SWX part.
What do you want to achieve?
Retrieving data ...