Give this a shot and maybe it is what you are looking for:
On the Actions menu select Actions
Click the Star icon on the right for a New action
Give it a descriptive name
Click the Star icon on the right again in the new window
In the 'Select Action Type' drop down choose 'Format Value'
[Field:] either select the field you want formatted or type in the name if it isn't listed
[Format String:] this is what you want the selected field to be when the action runs
Select the tracks you want formatted and under the Actions menu select for new action
[Format String:] %artist%
If it doesn't work the way you intended there is an undo button on the main menu (left pointing blue arrow). Play with it until you get it working the way you want. You can add many steps to one action but you must be careful that one action does not undo what you wanted. For example, I have an action that I named 'Master Format' that has 107 separate steps. Hope this helps and happy tagging.