A whole cell:
Code:
Range("A1").Font.Strikethrough = True
Part of the text of a cell:
Code:
Range("A1").Characters(Start:=3, Length:=4).Font.Strikethrough = True
In both cases, if the range is multicelled, contiguous or not, all the cells will be affected.
To toggle:
Code:
Range("A1").Font.Strikethrough = Not Range("A1").Font.Strikethrough