The text in a parameter control (other than the title) will be the same regardless of the font size.
The text that can be formatted and changed is the text that appears in a list of values, not in a type-in, date or single-value parameter.
OK, thanks guys.
How strange that this isn't possible. Hopefully it will be fixed in a future release.
Why have 4 years gone by and this still hasn't been resolved?