Hi,
If I get what you want, you would like to add an empty column in Power Query, load the Query into Excel, then use that empty column to add comments?
Well yes you can do that but your comments will not be linked to the rows.
If your rows have an ID, maybe you can create an extra table with 2 columns, ID and Comments, and copy paste the ID of each row you want to comment, then add your extra info.
Afterwards you could merge the queries if that's what you want.
Does that help?
Olivier.