Overwrite UTM Parameter

We do have some Campaigns (Google, facebook,...) When the user arrives the landingpage (abo.mysite.com) he does have the utm parameter utm_source=theCampaignSource. When the user clicks an CTA the CTA gives an new UTM utm_source=abo and he goes to shop.mysite.com.

We are not able to remove the UTM from abo.mysite.com.

Is there a way to check if a user have already an UTM, and when he does have one to kepp them until shop.mysite.com? So we know that the user is comming from Google (...)?

We know that how this Thing is set up is a very bad practice, and we are working on it.

Ive found a code snippet which is manipulating the links on a site:

links.forEach(function(link){
 link.setAttribute("href","abo.mysite.com")
})

but i couldn get it work - cause i do have a lack of experience.

Update

To my specific needs a made it that way:

1) Remove existing UTM from Links on the Site

<script>
var link = document.getElementsByTagName("a");

for (var i = 0; i < link.length; i++) {
    link[i].href = link[i].href.replace(/(\?)utm[^&]*(?:&utm[^&]*)*&(?=(?!utm[^\s&=]*=)[^\s&=]+=)|\?utm[^&]*(?:&utm[^&]*)*$|&utm[^&]*/gi, '$1');
}
</script>

2) Hash the UTM in the URL

 <script>
        if(!window.jQuery) {
          document.write('<script type="text/javascript" src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.2/jquery.min.js">\x3C/script>');
        }
     </script>

    <script type="text/javascript">
                $(document).ready(function() {
                function getUrlVars() {
                    var vars = [],
                        hash;
                    var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');
                    for (var i = 0; i < hashes.length; i++) {
                        hash = hashes[i].split('=');
                        vars.push(hash[0]);
                        vars[hash[0]] = hash[1];
                    }
                    return vars;
                }

                var parameters = getUrlVars();
                var utm_source = decodeURIComponent(parameters['utm_source']);
                var utm_campaign = decodeURIComponent(parameters['utm_campaign']);
                var utm_medium = decodeURIComponent(parameters['utm_medium']);
</script>

3)rewrite every URL on the Site with the hashed UTMs

<script>
          $('a').each(function(){
  $(this).attr('href', $(this).attr('href') + '?utm_source=' + utm_source + '&utm_campaign' + utm_campaign + '&utm_medium' + utm_medium);
});

            });

Edit Thanks to Michele Pisani

this works well - BUT, if a user does not have an UTM, and he clicks the button, the UTM will be set to undefined

Is there a way to set the UTM Parameter from the URL when the User already has one, or to use the existing UTM (which are hardcoded in the button) when he does not have an UTM in the URL.

Edit 2 & update Finally - with the help of you guys - i found a solution:

<script>
    var link = document.querySelectorAll('a:not([href*="#"])');    
    for (var i = 0; i < link.length; i++) {
        //link[i].href = link[i].href.replace(/(\?)utm[^&]*(?:&utm[^&]*)*&(?=(?!utm[^\s&=]*=)[^\s&=]+=)|\?utm[^&]*(?:&utm[^&]*)*$|&utm[^&]*/gi, '$1');
    }
</script>


    <script type="text/javascript">

    $(document).ready(function() {
        function getUrlVars() {
            var vars = [],
                hash;
            var hashes = window.location.href.slice(window.location.href.indexOf('?') + 1).split('&');
            for (var i = 0; i < hashes.length; i++) {
                hash = hashes[i].split('=');
                vars.push(hash[0]);
                vars[hash[0]] = hash[1];
            }
            return vars;
        }

        //var parameters = getUrlVars();
        //var utm_source = decodeURIComponent(parameters['utm_source']);
        //var utm_campaign = decodeURIComponent(parameters['utm_campaign']);
        //var utm_medium = decodeURIComponent(parameters['utm_medium']);
        var url_string = window.location.href; //window.location.href
        var url = new URL(url_string);
        //var c = url.searchParams.get("c");

        var utm_source = url.searchParams.get("utm_source");
        var utm_campaign = url.searchParams.get("utm_campaign");
        var utm_medium = url.searchParams.get("utm_medium");




        $('a:not([href^="#"])').each(function() {
            if(utm_source != "" && utm_source != null){
                var href = $(this).attr("href");
                href = href.replace(/(\?)utm[^&]*(?:&utm[^&]*)*&(?=(?!utm[^\s&=]*=)[^\s&=]+=)|\?utm[^&]*(?:&utm[^&]*)*$|&utm[^&]*/gi, '$1');
                $(this).attr("href",href);
                $(this).attr('href', $(this).attr('href') + '?utm_source=' + utm_source + '&utm_campaign=' + utm_campaign + '&utm_medium=' + utm_medium);
            }
         });


    });

    </script>

With JavaScript, to remove UTM parameters from links in page you can try this function with regex:

var link = document.getElementsByTagName("a");

for (var i = 0; i < link.length; i++) {
    link[i].href = link[i].href.replace(/(\?)utm[^&]*(?:&utm[^&]*)*&(?=(?!utm[^\s&=]*=)[^\s&=]+=)|\?utm[^&]*(?:&utm[^&]*)*$|&utm[^&]*/gi, '$1');
}

If you are using Google Tag Manager you can add it in a custom HTML tag and fires it on DOM Ready.