I need to change the shipping carrier drop-down and shipping method radio button once via a javascript function, not forever.

However, when I use this function, which executes when on the Review and Submit page when the order is < $5, it goes into an endless loop:

function setFreeSampShipping(){
 var options = document.forms[ checkout ].shippingcarrierselect.getElementsByTagName( option );
 for (i=0;i<options.length;i++){
  if (options[i].value ==  nonups ){
   document.forms[ checkout ].shippingcarrierselect.value= nonups ;
   document.forms[ checkout ].shippingcarrierselect.onchange();
   document.location.href= /app/site/backend/setshipmeth.nl?c=659197&n=1&sc=4&sShipMeth=2035 ;
  }
 }
}

It gets called from within this part of the function setSampPolicyElems() which you can see I ve commented out to stop the loop:

if (carTotl < 5 && hasSampp == 1) { 
    /*
    if (document.forms[ checkout ].shippingcarrierselect.value == ups ){
      setFreeSampShipping();
    }
    */
    document.getElementById( sampAdd ).style.display="none";
    document.getElementById("custbody_ava_webshiptype").value = "7";//no charge free freight
    if (document.getElementById("applycoupon")) {
        document.location.href= /app/site/backend/setpromocode.nl?c=659197&n=1&sc=4&kReferralCode=SAMPLE 
    } 
    document.write("<div id= msg ><strong>Sample & Shipping:</strong></span> No Charge. (Your sample order is < $5.)</div>");
}

To see the issue, go to the order review and submit page here: https://checkout.netsuite.com/s.nl?c=659197&sc=4&n=1 (or go to http://www.avaline.com, hit "checkout", and login)

You can log in with these credentials:
Email : test2@gmail.com
Pass : test03

My solution so far was to swap out the onchange() event trigger line with this, since then I m not running document.location.href twice: instead, I m passing the two variables in the one URL query string:

var dropdown = document.getElementById( shippingcarrierselect );
document.body.style.cursor =  wait ;
document.location.href= /app/site/backend/setshipmeth.nl?c=659197&n=1&sc=4&sShipMeth=2035&sShipCarrier= +dropdown.value;