Can I change non-test requests and settings with groovy?

Hello,

I was wondering if it's possible to run groovy scripts for setting up "normal" requests and settings?

I know you can add groovy scripts as test steps in test cases. However, I want to be able to run a groovy script for setting up my settings for my requests. For instance, I would like to set the http header for each request to include a userid and a password.

Thanks!