setting parameter values at scenario level

Hi,

I have a scenario with 20 groups on them. Each has a parameter set and used by the web_url functions to the value of a desired "hostname" on preproduction enviroment, e.g., wwwpre.x.x.uk. Is there a way this value could be change for all groups/scripts using the parameter? e.g. to wwwtst, wwwdev?

 

thanks