Cross-Field updates

Hello, 

Would it be possible to set-up cross-field updates on the same Module. 

We are updating Comment Log weekly, and it does show a great summary on the Opportunity, but cannot be added to the List view. 

We also have a Next Steps field that is a Text field that can be added to the List view. 

Is it possible to set up a BPM in the following way: when a new comment is added in the Comment Log that comment will be added to Next Steps field and replace the old comment? 

Thank you!

Ada