Here is a quick and dirty way to do this. Make sure you place this code right above the </body> tag in the "Login.aspx" file. You can customize this to suite your needs.

<script language="Javascript">
var t = document.getElementsByClassName("LoginError");
var c = t[0].innerHTML;
if (c.match("The maximum number of sessions has been reached.")) {

//add to existing matched error message

t[0].innerHTML += "&lt;p&gt;Please try your request later or contact us at (000)000-0000. We apologize for any inconvience this may have caused.&lt;/p&gt;";

//replace existing matched error message
//t[0].innerHTML = "The maximum number of Laserfiche licenses has been reached. Please try your request again in 5 minutes. If the problem persists please contact support at (000)000-0000";
}
</script>