Personally, I think I'd try to set up a worksheet that met all the requirements
for all users.  Then tell them not to change it.  If they change it, send it
back with a nasty note explaining that this isn't what you asked for.

If you can't do that, then I think that the only option left is to fix
everything manually each time you get something back.  If the users can add
columns anyway they want, I would guess that it would be difficult to come up
with a macro that is robust enough to do the conversion.

And you can always unlock the cells that require manual input and lock the cells
that shouldn't be changed (headers/formulas) and then protect the worksheet.

But worksheet protection is easily broken.

To protect unwanted changes to your worksheet from the average user, you must
use a combination of unprotecting the cells you want the user to change and
protecting your worksheet.

- Highlight the cells you want to allow users to change.
- Select Format>Cells>Protection
-     Uncheck the 'Locked' checkbox.
         These are now the only 'unlocked' cells
- When you've unlocked all the cells you want to allow users to change...
- Highlight the entire worksheet (left-click on the blank box above the 1 in
Row 1)
- Select Tools>Protection>Protect Sheet...
- Enter a password if desired
- Select OK

Done.
HTH,