True column-mode (block-selection and editing) text editor solution?

geany

is an integrated development environment that provides good column editing support which is worth checking out (an example here)

Simply put, press down Alt+Shift instead of just Shift while making selections to invoke column mode. One important limitation is that the edits in column mode are (as yet) not undo-able.

To achieve the same with the mouse, hold down Ctrl while selecting. This actually works with most Scintilla-based editors (including SciTE and Geany).

To edit columns, I use vi / gvim. This will take a bit of learning to get used to vi, but in the end many people find this to be their preferred editor.

Specifically within vi you can use CTRL-V to highlight columns in visual mode, then you can edit it as you would expect. I use this all the time for adding and removing comments, or indenting functions ie CTRL-V (highlight a column) SHIFT-I '#' ESC will comment out that entire column.

You do use the Eclipse editor. Alt+Shift+A should do what you need.