In excel 97, there was a shortcut button on the toolbar to insert the equal
sign in a cell to convert that cell into a formula without changing the
existing data on that cell (extremely useful shortcut for editing). Example
cell contains 12345 (a number) and I want to convert it to +12345-12 (a
formula). I used to be able to select this cell click on the equal sign
shortcut button and enter -12 to get the desire result.

I am currently using excel 2003 and that shortcut button is gone. There is
an option to customize the toolbar to get the equal sign shortcut but when I
click on this shortcut it erases the cell content and insert the equal sign
(not very useful).

Does anyone know of a way to insert the equal sign on a cell to convert it
to a formula without the need to edit this cell by pressing F2 to edit the
entire cell?