Emacs soft line wrap at word boundary

First, make sure your TERM is correct at each location:

• xterm-something (e.g. xterm-256color) inside your local shell running in your iTerm2 window
• xterm-something inside your shell after SSHing to the Linux system
  This should be the same as whatever you are using locally in iTerm2, since SSH should be passing it along to the remote side (and, importantly, the remote side should not be blindly overriding the value in a shell initialization file).
• screen-something (e.g. screen-256color) inside your shell running under tmux on the Linux system
  You should always use a screen-based TERM inside tmux.

Having an xterm TERM immediately outside tmux will allow tmux to recognize the modified arrow keys, but it will not pass them through unless you also have its xterm-keys window option turned on. Put this in your ~/.tmux.conf on the Linux system:

set-window-option -g xterm-keys on

The sequences for the shifted keys should now make it through to Emacs, running inside tmux, across an SSH connection, inside an iTerm2 window.

The easiest way to do this is with the rectangle commands.

Go to the first line of the buffer (or more generally the first line where you want to insert text) and move to the column where you want to insert the text. Go to the last line and move to the same column (there's no built-in way to do that). Type C-x r t (string-rectangle) and type the string you want to insert.

You can use the following function to move the cursor to the same column as the mark:

(defun move-to-mark-column ()
  (interactive "@")
  (move-to-column (save-excursion
                    (goto-char (mark))
                    (current-column))))

If you want to move to a column by number, there's move-to-column: C-u 42 M-x move-to-column RET. Unless you bind this to a key, it's shorter to move to the beginning of the line and then by character count (Home C-u 42 Right), but this can move to the next line if the count is too high, whereas move-to-column leaves you at the end of the line in this case. Also move-to-column behaves differently if there are tabs or split lines.

If the point and mark aren't on the same column, they're opposite corner of a rectangle. The rectangle command affect all the characters inside that rectangle. string-rectangle erases the rectangle and puts the specified text on each line instead. C-x r d erases the rectangle. You can also copy-paste (C-x r M-w, C-x r k, C-x r y to copy/kill/yank) and insert or fill with rectangles (C-x r o, C-x r c to open/clear with spaces), and more.