Hi, This is solution for that.

from openerp.osv.orm import setup_modifiers


def fields_view_get(self, cr, uid, view_id=None, view_type='form', context=None, toolbar=False, submenu=False):
            res = super(uma_stock_picking_in, self).fields_view_get(cr, uid, view_id=view_id, view_type=view_type,
                                                                    context=context, toolbar=toolbar, submenu=submenu)
           if view_type == 'form':
                    doc = etree.XML(res['arch'])
                    for node in doc.xpath("//field[@name='min_date']"):
                            node.set('readonly', "0")
                            setup_modifiers(node, res['fields']['min_date'])

                    res['arch'] = etree.tostring(doc)
            return res

You should notice function setup_modifiers if you want to set option in ['invisible', 'readonly'] because in version 7 when you set readonly or invisible it will generate the modifiers attribute to take care this.

Cheer.