This question was cross-posted to http://answers.awesomium.com
For the benefit of other users, I'm documenting the cross-post's answer from Awesomium's lead developer, Perikles C. Stephanidis:
As it's been discussed in many similar posts:
You cannot change WebPreferences of a WebSession after the session is created.
You cannot change the WebSession of a view (WebControl) after the view is created. So this simply means that in order to change any of the preferences specified for a session and use them with a view, you need to create a new WebSession with the new preferences, and a new view (WebControl) that uses this new session. There is no other way.
To do this programmatically using the WinForms WebControl, see:
Using Web-Sessions - Assigning to a WebControl programmatically