Alt
+Shift
+DownKey
to box-select beginning of each string followed by Ctrl
+V
pastes only on the first line.
Can you select your column with Alt+Shift+Down, type in a single unique character then use Search+Replace to get your text inserted the way you want?
1) Mark
2) Push Alt+c
to open Column editor
3) Enter text there
As commented by @chapo it now works fine with Alt-Shift-Down
and then pasting.