Because I cannot post my actual code I have ginned up a simplified example that demonstrates my intent. Lets say I have a simple CGI script that generates HTML with a little javascript inline.
test.cgi

use strict;
use warnings;
use CGI;
use CGI::Carp qw(fatalsToBrowser);

local our $cgi = new CGI();

my @F_NAMES = ("a","b","c");
my @S_NAMES = ();

print $cgi->header();
print qq(
    <script src='https://blah.blah.js'></script>
    <script type='text/javascript' language='javascript'>
    var xml;
    var xmlObject;
    var param;
    
    function do_Work()
    {
        var what  = document.getElementsByName('FIRST_SELECTION')[0].v
+alue;
        var test  = document.getElementsByName('SECOND_SELECTION');
        for(i = 0; i < chec.length; i++)
        {
            if(chec[i].checked == true)
            {
                type=chec[i].value;
            }
        }
        var build = document.getElementsByName('Build_ID')[0].value;
        alert(what+" "+test);
        xmlObject = loadXMLHttpObject();
        alert(xmlObject);
        xmlObject.onreadystatechange = function(){
           if(xmlObject.readyState == 4)
           {
                if(xmlObject.status == 200)
                {
                    alert(xmlObject.responseText);
                    //Some kind of assignment statement using document
+.getElementsByName???                   
                }
           }
        }
        xmlObject.open("POST", "https://blah_blah.blah2.cgi", true);
        param = "get_stuff&cmdnV="+what;
        xmlObject.send(param);
    }
    </script>);
print
    $cgi->table({-border=>1,
                 -cellpadding=>'1',
                 -cellspacing=>'0',
                 -width=>'100%',
                 -bgcolor=>'whitesmoke'}),
    $cgi->Tr($cgi->td({-colspan=>3, -align=>'center'},
        "<b>First Name(s):</b><br>",
        $cgi->scrolling_list( -name => 'FIRST_SELECTION',
                              -values  => [@F_NAMES],
                              -size    => 1,
                              -default => 'none',
                              -onChange=> 'do_Work();')),
    $cgi->Tr($cgi->td({-colspan=>3, -align=>'center'},
        "<b>Second Name(s):</b><br>",
        $cgi->scrolling_list( -name => 'SECOND_SELECTION',
                              -values  => [@S_NAMES],
                              -size    => 5,
                              -default => $S_NAMES[0]));
[download]

The javascript calls another cgi using some ajax, and according to the alert, returns the proper data.
I would like to assign that returned data to the scrolling_list with the name 'SECOND_SELECTION'; the theory being that for every element in @F_NAMES there is a number of unique entries for @S_NAMES and the user will need to populate the second scrolling_list with @S_NAMES. Is there a way to make such an update using the DOM and the javascript function do_Work()? Perhaps javascript and perl? I can not seem to find an ID for any of the DOM objects.

Thank you Kindly