No; users of the style cannot override this. It may only be defined in the style.
|monlong||Month. Long form. Example: January, February, March...|
|monshort||Month. Short form. Example: Jan, Feb, Mar...|
|yy||Year, two digit.|
|yyyy||Year, four digit.|
|weeks||All the weeks for this month, consisting of a bunch of CALENDAR_WEEK variables.|
|urlmonthview||The URL to a page showing all posts in this month, by subject.|