The generators operate using Zim program templates. You can edit these files to change the code that is generated. However, any changes you make affect all users of Zim since they use the same templates.
One kind of change that does not adversely affect other users is the inclusion of new user code customization points. When you insert new places for user code, you should follow the rules described above and select a name for the new code section that is unique within the template.