I make extensive use of independent test cases and the "Run TestCase" test step to modularise tests. I'm not sure if I understand your use case exactly but I hope this helps...
If I have two "sub" test cases and I want to pass a value from the first case to the second, I will create a test case level property in both the sub cases, then in the first one I will set this property, effectively making it an output property.
Important, when you call test cases that returns properties you must configure this in the calling "Run TestCase" step:
Remember to tick the properties that are return properties.
Then I have the second test case where the test case level property is effectively an input property.
In my "calling" test case, the one orchestrating the sub common test cases, I then use a Property Transfer Test Step to copy the property in question. The transfer test step will look something like:
Overall the project will look something like:
Notice how I've moved my common test cases to a separate test suite for convenience.
