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<IfModule mod_deflate.c>
    AddOutputFilterByType DEFLATE application/javascript text/css text/html text/xml
</IfModule>

# Note: You are able to choose a different name in the Admin CP. If you've done that you need to change it here too
<Files "error.log">
    Order Deny,Allow
    Deny from all
</Files>

I have changed the name of default Admin folder to something else, do I have to do anything here.
What does the line below mean.
# Note: You are able to choose a different name in the Admin CP. If you've done that you need to change it here too.

The first part sets up the compression for defined filetypes (JavaScript, CSS, HTML, XML);
the second one disables access to error.log files (default name) where various debug information are saved if the Error Logging Medium setting (Server and Optimization Options) is set to Log errors or Log and email errors.
You do not have to modify this file if you have changed the ACP path.