Joomla creates a generator meta tag automatically. If you view source of your joomla site you can search for meta tag “generator”. The default generator tag looks like
<meta name="generator" content="Joomla! 1.5 - Open Source Content Management" />
We can modify this generator tag and also can put option in our custom joomla template to change this meta tag to site name or something different. so let’s start 
In you template index’s file header tag you can write a line like bellow
<?php
$this->setGenerator("your custom generator name");
$this->setGenerator(""); // you can leave that as blank too
?>
We can set a option in template
in template index.php file
<?php
$myconfig = new JConfig();
$mysitename = $myconfig->sitename;
?>
<?php
if($this->params->get('removegeneratortag') == "yes"):
// Remove the generator meta tag
$this->setGenerator($mysitename);
endif;
?>
in params.ini file add extra line
removegeneratortag=yes
in templateDetails.xml file
<params>
<param name="removegeneratortag" type="list" default="yes" label="Remove Joomla Generator Tag" description="Remove or disable joomla generator tag from head tag for security reason">
<option value="yes">Yes</option>
<option value="no">No</option>
</param>
</params>
before
"</install>"'
tag
you are done. I think now you can add/customize in your own way as you need. If you don’t know how to modify the above code then don’t try 
Thank you