user3503851, Dreamweaver has a notoriously shoddy regex flavor. Nevertheless, here is a working example, tested in CS6.
Our test text:
My Untitled Document Is Here
My Beautiful Document Is Here
My Document, the Beautiful
The goal: replace "Document" with "Blog", but only in a line that contains the word "Beautiful"
Search: ((?=.*?Beautiful)[^\r\n]*)(Document)
Replace: $1Blog
Result:
My Untitled Document Is Here
My Beautiful Blog Is Here
My Blog, the Beautiful