I am utilizing a custom search where I've got a dropdown:

<select name='Time_Available'>
            <option value="" selected='true'>Any</option>
            <option value='<?php echo date('Y/m/d', strtotime('+30 days')) ?>'>30 days</option>
            <option value='<?php echo date('Y/m/d', strtotime('+60 days')) ?>'>60 days</option>
            <option value='<?php echo date('Y/m/d', strtotime('+90 days')) ?>'>90 days</option>
            </select>

Although, once the form is posted, when the "Any" choice is selected, I wish it to add this towards the form:

<input type='hidden' name='Model' value='Yes' />

For that relaxation from the options (30, 60, 3 months) Among the finest it to submit regularly with no above part.

I had been attempting to deal with this with the addition of &Model=Yes to the need for "Any" even though ampersand will get messed up. Can there be any javascript or jQuery I'm able to increase resolve this?

It isn't difficult.

Add the hidden-input towards the form and customize the choose into this:

<select name='Time_Available' onchange="this.form.Model.disabled=(this.options.selectedIndex)? true:false">

When the selected option changes, and also the new selected option isn't the first one, the get's disabled.

jQuery can perform this in five seconds. You will find more complicated ways to achieve the input put into the page, however i recommend you simply place it there within the HTML without JS intervention:

<input id="Model" type="hidden" name="Model" value="Yes" disabled="disabled" />

Then you definitely simply do this.

$("select").change(function () {
   if ($(this).val() == 'Any') {
      $("#Model").attr('disabled', '');
   }
   else {
      $("#Model").attr('disabled, 'disabled');
   }
});

Observe that if "Any" is chosen automatically, you won't want to disable Model initially for apparent reasons.

Incidentally, I am a little confused why you'll need one more check if you're already checking the need for the choose. Rather than your script checking Model == Yes, why don't you just check Time_Available == Any?

Finally, you can't append towards the query string in the manner you describe (just adding &lifier to values like that's not likely to work). The ampersand is going to be encoded instantly. If customers could just add anything they felt prefer to the query string in a way it might be a UI nightmare.