Remove element(s) from QUERY_STRING

I need to remove/replace selected pieces of the QUERY_STRING without knowing what the rest of it contains. My basic idea right now is to explode("&") it into an array, removing (or modifying) the relevant array elements and then implode("&") it again. The main problem is finding the right element to remove/replace - I can't find any array_find function. I will use this to maintain a set of variables over subsequent calls to a collection of php scripts. I can't use session variables because: (1) I use several scripts. (2) I need to be able to change the values of the variables (they are search parameters and general state stuff). Also, I'd like to avoid cookies whenever possible. Is there an easy or better way to do this?