vertical-cooperative/easy_my_coop_be/models/partner.py

from odoo import fields, models


class ResPartner(models.Model):
    _inherit = 'res.partner'

    legal_form = fields.Selection(selection_add=[('scrl', 'SCRL'),
                                                 ('asbl', 'ASBL'),
                                                 ('sprl', 'SPRL'),
                                                 ('sa', 'SA')])