How to change template file name and destination for some blocks?
Check out template_preprocess_block. You can do this with the following code in your theme's template.php file:

function MYTHEME_preprocess_block(&amp;$variables) {
  // Perform a check based on any parameter, e.g. block ID.
  if ($variables['block_html_id'] == 'block-system-main') {
    // This will lookup for block--system-main-block.tpl.php file in your
    // theme.
    $variables['theme_hook_suggestions'] = 'block__system_main_block';
  }
}


However, Drupal already looks for various template names, before it settles down for the default block.tpl.php. Here is the list:


block--block--[block-id].tpl.php
block--[module]--[delta].tpl.php
block--[module].tpl.php
block--[region].tpl.php
block.tpl.php


See this page for more information.