Ctrl-Alt-2 is not a standard Windows shortcut for anything in an English-language system. If it does something on your system, that's because your keyboard has been programmed for it or it uses a non-an English-language. In an English-language system, Word has its own 27 built-in Ctrl-Alt keyboard shortcuts:
Ctrl-Alt-1 - Apply the Heading 1 style
Ctrl-Alt-2 - Apply the Heading 2 style
Ctrl-Alt-3 - Apply the Heading 2 style
Ctrl-Alt-C - Insert a copyright symbol
Ctrl-Alt-D - Insert an endnote
Ctrl-Alt-F - Insert a footnote
Ctrl-Alt-I - Switch to print preview
Ctrl-Alt-K - Start AutoFormat
Ctrl-Alt-L - Insert a LISTNUM field
Ctrl-Alt-M - Insert a comment
Ctrl-Alt-N - Switch to Draft view
Ctrl-Alt-O - Switch to Outline view
Ctrl-Alt-P - Switch to Print Layout view
Ctrl-Alt-R - Insert a registered trademark symbol
Ctrl-Alt-S - Split/Unsplit the document window
Ctrl-Alt-T - Insert a trademark symbol
Ctrl-Alt-V - Paste special
Ctrl-Alt-Y - Repeat Find
Ctrl-Alt-Z - Switch between the last four edits
Ctrl-Alt-. - Insert an ellipsis
Ctrl-Alt-- - Insert an em dash
Ctrl-Alt-F1 - Display System Information
Ctrl-Alt-F2 - Display File Open Dialogue
Ctrl-Alt-Home - Open a list of browse options
Ctrl-Alt-PageDown - Move to the end of the window
Ctrl-Alt-Shift-PageDown - Extend a selection to the end of a window
Ctrl-Alt-Shift-S - Open the Styles task pane

Any others that you might have or might have had would have to have been assigned by you - in Word.

As you can see from the above list, by default, Ctrl-Alt-2 in Word applies the Heading 2 style; it does not insert the @ character.
Not very clever, in my view. In any event, wiping out a keyboard shortcut merely tells it to do nothing, not to do something else...

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]