You can do this with Notepad++ and Block-Selection in like 1,2 Minutes:

- Paste the original list

- Block-Select (Alt + Pressed Mouse1) a block-line behind (trailing) all entries; I admit this step is hard to describe with words, but currently im unable to provide an image/video

- Paste "https://news.ycombinator.com/item?id="

- Block-Select all ids from original list and paste it at the end

- You may be finished now or you can Regex-Replace " +" with " " to remove the long spaces between the link title and the link itself.

Block-Selection + Copy-Paste is amazingly fast for doing things like that.