If these cells are in a range that contains numbers only, you could do
the following:
Select the range that includes the zero cells.
Choose Edit>Replace
For 'Find What', enter a zero
For 'Replace With'
Click the Options button
Add a check mark to 'Match entire cell contents'
Click Replace All
Click Close
With the cells still selected, choose Edit>Go To
Click Special
Choose Constants
Remove check marks from Numbers, Errors, and Logicals, and
leave Text checked
Click OK
