I'm not sure if I understand exactly what you are asking. Are you saying that you've written some external Groovy scripts and have them in a directory that is referenced as a Script Library?
If so you can specify a project script library in the project properties. When doing this you can specify paths relative to the project file, by using the ${projectDir} property.
For full information on specifying relative paths to project resources, please review the following documentation page:
https://support.smartbear.com/readyapi/docs/testing/best-practices/root.html