Hi Felipe,
You are correct that accessing SSC via the SDK (or using the PySAM Python package) does not give you access to the internal models. It does give you access to the same SSC inputs and outputs as the SAM desktop application.
SAM is an open source project written in C++, so it is possible to build your own version of SAM (and/or SSC) with modifications to the internal models. However, the code structure is complex, and the models do not have detailed documentation designed to facilitate these types of modifications.
You can find the SAM code repositories and build instructions on GitHub:
github.com/NREL/SAM
Best regards,
Paul.