Ok, here is the complet solution.

I have defined two differents file : pos_as.xml and pos_cf.xml

I have declared those two files in __openerp__.py file (https://www.odoo.com/fr_FR/forum/help-1/question/could-we-define-multiple-files-in-the-qweb-section-of-the-openerp-py-91576)

In the pos_as.xml, I have declared <t t-name="PosTicket_as">
In the pos_cf.xml, I have declared <t t-name="PosTicket_cf">

I have created a new file : /pos_lapagept/static/src/js/screens_all.js

I have included this file with :

    <template id="pos_lapagept.assets_backend_all" name="point_of_sale assets" inherit_id="point_of_sale.assets_backend">

        <xpath expr="//script[contains(@src,'models.js')]" position="replace">

            <script type="text/javascript" src="/pos_lapagept/static/src/js/models_all.js"></script>

            <script type="text/javascript" src="/pos_lapagept/static/src/js/screens_all.js"></script>

            </xpath>

    </template>

In the file screens_all.js :

            openerp.pos_lapagept = function (instance) {

                    var _t = instance.web._t,

                    _lt = instance.web._lt;

                    var QWeb = instance.web.qweb;

                    instance.point_of_sale.ReceiptScreenWidget.include({

                            refresh: function() {

                                    var order = this.pos.get('selectedOrder');

                                    var user_template = 'PosTicket';

                                    if(instance.session.uid == 21){

                                            user_template = 'PosTicket_as';

                                    } else if (instance.session.uid == 53 || instance.session.uid == 55 || instance.session.uid == 56 || instance.session.uid == 57 ) {

                                            user_template = 'PosTicket_cf';

                                    }

                                    $('.pos-receipt-container', this.$el).html(QWeb.render(user_template,{

                                                        widget:this,

                                                        order: order,

                                                        orderlines: order.get('orderLines').models,

                                                        paymentlines: order.get('paymentLines').models,

                                        }));

                            },

                    });

            }

THANKS TO AXEL!!!