Reply To: Use document name without extension and a grep question

InDesign treats the text variables as a single character so you can only apply formatting to the whole string.
As InDesign treats variable text as one character you can get some strange effects if the text box is too small, try it make the text box very short and see how the characters sit on top of each other, the text will not wrap to more than one line etc.

The only way around this is, as you say, to convert it to text, then you can format it the same as any other text.