Override php and html t() strings.

Hi,

I am bit confused how to achieve this. there is a string in the comment module like this:

return t('<a href="@login">Log in</a> or <a href="@register">register</a> to post comments', array('@login' => url('user/login', array('query' => $destination)), '@register' => url('user/register', array('query' => $destination))));

I want to override only the part "to post comments" to "to post reviews"
How do I go about this?

Thanks for your help,
Perry.