Hello Jose,
that block is a fundamental RLC block so it cannot be customized. You could customize the dynamic three phase load block instead. However, you might not even need to customize it as it might do what you are looking for.
Depending on what you are doing, you might want to switch to using simscape instead of specialized power systems. For most utility based simulaiton, I would prefer specialized power systems, but specifically for dynamic loads, simscape is often easier to use. This has to do with the fact that simscape can implement a time varying resistance, while specialized power systems can only mimic the behavior.
Regards,
Joel
