What scripting language are you using? I believe it's possible in at least JScript and DelphiScript to implement "optional" parameters. In JScript, I think you can just check to see if the parameter value is null and, if it is, assign a default value. In DelphiScript, you assign the default value in the parameter declaration. I'm not sure if VBScript supports "optional" parameters.
The advantage to this is that you then don't need to update any of your "legacy" tests as the default values will then be used for your new parameter.
As far as I know, though, there's no "find and replace" in Keyword tests... you need to manually update them all unless there's a feature that I'm not aware of (SmartBear support can confirm availability).
