You can modify a sheet via code by taking these actions
In code this would be:
Sub UnProtect_Modify_Protect()
ThisWorkbook.Worksheets("Sheet1").Unprotect Password:="Password"
'Unprotect
ThisWorkbook.ActiveSheet.Range("A1").FormulaR1C1 = "Changed"
'Modify
ThisWorkbook.Worksheets("Sheet1").Protect Password:="Password"
'Protect
End Sub
The weakness of this method is that if the code is interrupted and error handling does not capture it, the worksheet could be left in an unprotected state.
The code could be improved by taking these actions
The code to do this would be:
Sub Re-Protect_Modify()
ThisWorkbook.Worksheets("Sheet1").Protect Password:="Password", _
UserInterfaceOnly:=True
'Protect, even if already protected
ThisWorkbook.ActiveSheet.Range("A1").FormulaR1C1 = "Changed"
'Modify
End Sub
This code renews the protection on the worksheet, but with the ‘UserInterfaceOnly’ set to true. This allows VBA code to modify the worksheet, while keeping the worksheet protected from user input via the UI, even if execution is interrupted.
This setting is lost when the workbook is closed and re-opened. The worksheet protection is still maintained.
So the 'Re-protection' code needs to be included at the start of any procedure that attempts to modify the worksheet or can just be run once when the workbook is opened.