In odoo v12, we have field parameter named config_parameter="" in res.config.settings model. 

do_not_use = fields.Boolean(
config_parameter='model_name.do_not_use
)

In other versions, we can use set_param method in res.config.settings and use that to create a new record.

Hi Jean: You can create a system parameter from python like this:

self.env['ir.config_parameter'].sudo().set_param('<name of system parameter>', <value of system parameter>)

Yes, you can add the default value from python itself like this : 

self.env['ir.config_parameter'].sudo().get_param('your_module.your_field', default='[]')

The "[]" is best to use if you are using many2many fields. You can set your own default based on value you need.

Best regards

Altela (altelasoftware.com)