Yeh I don't think you can do that.
But with Data Merge you have the option to remove blank lines
I don't know about automatically replacing words without user interaction though...
How would that work, you could have for example
"The Doors walked in the doors" - and it would change to - "The Windows walked in the windows"
This seems like an odd request.
So if a customer enters "door", the Indesign template can replace it with "window". Prior to the operators opening and printing the document (zero interaction on their part).
Can you just not trust your operators to run some standard "search-and-replace" routines before proceeding?