How to overide the geo IP Redirect - .htaccess

Question

I currently have a Geo-redirect set up in my htaccess to redirect user say from Asia who visits example.com to asia.example.com. I am now wondering how to override that redirection so users from asia.example.com can get to example.com through a link on asia.example.com.
Is that possible or do I have to use a client-side redirect and how would I go about setting that up.
And some background info example.com is running Magento and asia.example.com will be a landing page for now.
Thanks
Update: My host says I should install this https://github.com/maxmind/GeoIP2-php on Magento... How would I do that?
Update from comment:
# Redirect multiple countries to a single page
RewriteEngine on
RewriteCond %{ENV:GEOIP_COUNTRY_CODE} ^(VN|SG|CN|MY|JP|KP|KR)$
RewriteRule ^(.*)$ asia.example.com$1 [R,L]

Answer 1

Normally Magento offers a store switcher in the form of a select field, see it working on demo.magentocommerce.com. The theme in use might change how this is displayed, it could be a link or button instead but the principle is the same, a store cookie is written with the store code as it's value. We can test for that directly in .htaccess and avoid GeoIP if present.
# Redirect multiple countries to a single page
RewriteEngine on
RewriteCond %{ENV:GEOIP_COUNTRY_CODE} ^(VN|SG|CN|MY|JP|KP|KR)$
# New cookie condition goes here
# ! means true when it doesn't match
# \b means word boundary
RewriteCond %{HTTP_COOKIE} !\bstore=default\b
RewriteRule ^(.*)$ asia.example.com$1 [R,L]
It is necessary for the cookie to be transmitted on every request or the user might find themselves being redirected later. You may have to set the cookie domain to .example.com (note the leading period) if it misbehaves. You can do this in Magento's admin under System > Configuration > Web > Session Cookie Management. This allows the cookie to be written by asia.example.com and be read by example.com, and vice versa.
If you want to make a link instead of the store switcher then use Mage::getUrl in this way, it will generate an URL with a ___store query parameter:
<?php
$url = Mage::getUrl('', array(
'_store' => 'default',
'_store_to_url' => true
));
?>
<?php echo $this->__('International Store') ?>