Support for other Banks?

First, you have to check if your bank propose an ATOS credit card payment system.

If yes, you have to know what is the demo merchant_id your bank use.

And then, in the module :

in uc_atos_get_mid(), you have :

  $banks_mid = array(
    'etransaction' => '013044876511111',
    'sogenactif' => '014213245611111',
    'cyberplus' => '038862749811111',
    'mercanet' => '082584341411111',
    'scellius' => '014141675911111',
    'sherlocks' => '014295303911111',
    'webaffaires' => '014022286611111',
  );

You have to add an entry for your bank in that array

And, in uc_payment_method_atos()

      $form['uc_atos_bank'] = array(
        '#type' => 'select',
        '#title' => t('Bank'),
        '#description' => t('Choose your bank ATOS solution provider.'),
        '#options' => array(
          'etransaction' => t('Credit agricole (E-transaction)'),
          'sogenactif' => t('Societe generale (Sogenactif)'),
          'cyberplus' => t('Banque populaire (Cyberplus)'),
          'mercanet' => t('BNP Paribas (Mercanet)'),
          'scellius' => t('La poste (Scellius)'),
          'sherlocks' => t('LCL : Le Credit Lyonnais (Sherlocks)'),
          'webaffaires' => t('Crédit du Nord (Webaffaires)'),
        ),
        '#default_value' => variable_get('uc_atos_bank', FALSE),
      );

You add an entry for your bank for the form setting page, and that all.

You can then submit a patch to see your change applied to the next version of that module.