Opencart Module CNPJ 2.0 modification

I need to make some modifications on a module called CNPJ 2.0 for version 1.5.4.1. This module is a new register page, where we got a Pessoa Fisica and Pessoa Juridica register form (by selecting one or other, fields are show and hidden). You can see my register page here to see what i am saying: [login to view URL] Things to be done in this module: 1. Create a new field when Pessoa Fisica is selected, called RG and make it required. 2. Create a third option, called Pessoa Jurídica ISENTA. 3. When Pessoa Jurídica is selected, make fields Razão Social and Inscrição Estadual required (only Razão Social is required now). 4. When Pessoa Jurídica ISENTA is selected, make Razão Social required and field Inscrição Estadual read-only and filled with the word ISENTA. 5. As we will have this 3 customers groups registered in OPENCART ADMIN and we will have different prices for each customer group, i want that this selection by customer on register form automatically set customer group in it record.