Script to toggle internet sharing using Alfred
You could try this (tested on OSX 10.9.5 but it may depends on the version of you OS) :

tell application "System Preferences"
-- display system preferences window
activate
-- wait to see the window
delay 1.5
-- try again
activate
-- Open sharing tab (or pane)
set current pane to pane "com.apple.preferences.sharing"
-- we want to see it
delay 1.5

tell application "System Events"
    tell process "System Preferences"

        -- click the checkbox to enable internet sharing
        tell window 1 to click checkbox 1 of row 8 of table 1 of scroll area 1 of group 1
    end tell
end tell
-- wait to see the result
delay 1.5
--quit -- we can quit system preferences
end tell