Change the .htaccess filename for a specific Virtual Host:

1. Open up your MAMP vhost conf file:

vi /Applications/MAMP/conf/apache/extra/httpd-vhosts.conf

2. Use the AccessFileName directive with your desired new filename for .htaccess in each Virtual Host:

<VirtualHost *:80>
	DocumentRoot /Applications/MAMP/htdocs
	ServerName localhost
	AccessFileName _.htaccess.testing
</VirtualHost>

The above virtual host would now use _.htaccess.testing as its .htaccess file, if it exists.

Globally change the .htaccess filename in MAMP:

1. Open the Apache config file in MAMP:

vi /Applications/MAMP/conf/apache/httpd.conf

2. Scroll down to for the AccessFileName derective and enter your new .htaccess filename.

All you need to do now is to restart Apache in MAMP and the new setting will take effect.