By default, Microsoft Excel uses the system separators that are defined in the regional settings in Control Panel. If you sometimes need to display numbers with different separators for thousands or decimals, you can temporarily replace the system separators with custom separators.
Click File > Options.
On the Advanced tab, under Editing options, clear the Use system separators check box.
Type new separators in the Decimal separator and Thousands separator boxes.
Tip: When you want to use the system separators again, select the Use system separators check box.
Note: For a permanent solution, you must change the regional settings in Control Panel.