If it is such modified metamaterial, you can directly use this method to extract the effective material peoprties, regardless its geometry. If it has substrate, you will need a second simulation to get S12 and refer to Smith's paper to use another formula, as the example is for symmetry case.
Basically it is based on amplitude transmission/reflectio coefficent to retrace the effective data. You can also refer to the Fresnel coefficients for a cavity.
I am not sure what do you mean offline. Depending on your license type, it may work without internet connection. You can download the example file and save on to your local machine.