Answering here to the initiated question.
You need understanding of any basic programming/scripting, OOP capability/knowledge, REST/Http/Https and JSON/XML.
Don't worry it's all easy, first double click on any test case/suite, you will see it's editor, in that there is a option for "setup script" for before running tests.
Please analyze what all variables on top are listed, like : runner/testRunner, testCase/testSuite, logger, context...etc.
There are methods from which one can get another handle, like from testCase you can get testSuite/teststep via respective methods, so those you need to know.
The idea is to run a testCase/Suite/Step by script, which you already have configured, you can set header for each api and also properties too. You can even do almost everything via Groovy/JavaScript scripting in soapui.
I am actually going to create a blog having required groovy scripts to do automation regarding, REST API execution and testing.
I will be posting that link here.
Thanks!