- You enter a 'set field in current item' action to your Workflow,
- click on 'Field' and select 'Title',
- click 'Value' followed by '...' and enter (without the quotes) "There should be a backslash after this: \ and two after this: \\" and
- add a lookup value by clicking the "Add or Change Lookup" button; for the 'Data Source' keep it on "Current Item" and in 'Field From Source' select "Modified by" (or any other lookup item)
"There should be a backslash after this: and two after this: \ domain\alias"
For the existing example the dynamic string for the Workflow action has to be specified as:
"There should be a backslash after this: \\ and two after this: \\\\"