Hi Ashton, you did post this late Friday and I don't think anyone is active over the weekend :)
You don't need to build a custom macro to get the query string from URL. Instead of using the rule wizard, use the CODE tab to write macro to get query string.
For example, on pages with URLs like /Home.aspx?keyword=kentico, {% keyword%} resolves into 10. Alternatively, you can get the values of query string parameters inside standard macros: {% QueryString.keyword |(identity)GlobalAdministrator%}