Obtaining var,inserting into url Multi Domains

What is the best way to handle this situation? Any guidance is greatly appreciated.

Want to retreive username variable from a .htaccess file and rewrite/insert variable into mutli domain links when clicked at the “t2=username place within each link?

user logs in/authenticates/redirects to:

[url]www.testdomain.com[/url]

this domain contains many url hyperlinks with &t2=username in the url strings of various domains at various places in each string (e.g [url]http://www.store1&t2=username[/url], [url]http://www.store2&08098&type2&t2=username[/url], etc).

Thanks
Zoe2 :p

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