It was an answer for a question on the Grasshopper3d forum (see the thread here), so I thought of tidying up the code and posting it here (probably just to convince myself that I still have the time to be posting things).
Not much to say, just change how your curves look in the rhino viewport through Grasshopper. I am sure that someone might find it useful.
Code in Python below and the file as usual at the [Sub]Code page.
#[Dynamic Display Attributes] was written by Marios Tsiliakos on 21 / 06 / 2015 in grasshopper 0.9.0076 #This definition is for the pubic domain feel free to use it , share it and modify it, by providing proper citing. #The author, Marios Tsiliakos of digitalsubstance.wordpress.com , makes no warranty, expressed or implied, #as to the usefulness of the software and documentation for any purpose.If this tool is used for commercial purposes please notify the author. #This work is licensed under a Creative Commons Attribution-Share Alike 3.0 #for more information visit www.digitalsubstance.wordpress.com. import Rhino.Display as rd # create some empty arrays display_modes =  display_modes_names =  #retrieve the list of Display modes on the document display_modes = rd.DisplayModeDescription.GetDisplayModes() #find out their names for i in range(len(display_modes)): display_modes_names.append(display_modes[i].EnglishName) #pick the display style that you want for j in range(len(display_modes)): if display_modes_names[j] == mode: disp_index = j else: continue selected_mode = display_modes[disp_index] if execute == True: selected_mode.DisplayAttributes.CurveThickness = width rd.DisplayModeDescription.UpdateDisplayMode(selected_mode) print("Changed the display option settings for visual style : " + y) else: selected_mode.DisplayAttributes.CurveThickness = 1 rd.DisplayModeDescription.UpdateDisplayMode(selected_mode) print(y+ " Display style reset to default settings")