Unfortunately there is no one-step method for renaming attribute values, however 7.2 does make it somewhat easier to edit multiple tasks simultaneously.
Here's how I would rename 'Work' to 'Word' in 7.2:
1. Add 'Word' to one of the 'Work' items
2. Filter by 'Word' and 'Work'
3. Switch to the 'List View' so you won't see any un-matching parent tasks
4. <Ctrl+A> to select all of the filtered tasks
5. Deselect 'Work' and select 'Word' in the attribute droplist
6. Delete 'Work' from the attribute droplist
In the future I can see myself adding a one-step menu option but not right now.