Increase the number of Undo levels in Excel
To change the number of Undo levels, follow these steps:
1. Launch Registry Editor.
2. In the Registry Editor, navigate to the HKEY_CURRENT_USER\
3. Right-click in the right pane and choose New -> DWORD (32-bit) Value:
Registry Editor creates the new value with a name such as New Value #1 and selects this name for editing.
4. Type the name UndoHistory over the default name and press Enter to apply the name.
5. Press Enter to display the Edit DWORD (32-bit) Value dialog box:
6. In the Value Data text box, enter the number of Undo levels you want from 0 to 100, hexadecimal base (256 actions - the biggest number, decimal base).
7. Click the OK button to close the Edit DWORD (32-bit) Value dialog box.
8. Choose File -> Exit to close Registry Editor.
9. Close Excel if it's running, and then restart it to make the changes take effect.
See also this tip in French: Comment augmenter le nombre de niveaux Annuler dans Excel.