Conditional Formatting in CubeView in the "annotation" or other "Text" cell

If you set the UD8 to Return a 1 if an explanation or 0 if not required.

Then set up a Delimited List Parameter where 1, 0 are the values and your Explain / Not Required text strings are the Display items.

Then set your CV column up to use this Combo Box as follows, note Modify Data = False means the cell will not allow drop down.

The cell value in the Cube View will display as Explain / Not Required but the cell amount will actually be 1 / 0 allowing you to perform conditional formatting.