You can use the Linework tool to change the line style for edges in a linked model. 
To do this, you must set the view’s visibility property for the linked model to By host view. 
- In the host model, open the view in which you want to change line styles. 
- Type VG, or click View tab Graphics panel Graphics panel  (Visibility/Graphics). (Visibility/Graphics).
- In the Visibility/Graphic Overrides dialog, click the Revit Links tab. 
- For the linked model, if the Display Settings value is not By Host View, do the following: - Click in the Display Settings cell. 
- In the RVT Link Display Settings dialog, on the Basics tab, select By host view. 
- Click OK twice. 
 
Now you can use the Linework tool to change the line style of edges in the linked model. See Use the Linework Tool.