Preventing format from being called on a subsearch

Hello,

I have a macro (a subsearch enclosed in square brackets) that I use to filter my initial search. I would like to do some regex magic on the search string that format creates. Unfortunately, if I call format and do parsing on the search field, a second format seems to be implicitly called at the end of the macro, and it encloses the regexed search string in an extra set of quotes and double parentheses, which confuses the outer search. Is there a way either to prevent format from being called at all, or to keep it from enclosing the field in quotes?