I\'ve got this code:
Try this:
function DisablePinchZoom()
{
$('meta[name=viewport]').attr("content", "");
$('meta[name=viewport]').attr("content", "width=yourwidth, user-scalable=no");
}
function myFunction()
{
$('meta[name=viewport]').attr("content", "width=1047, user-scalable=yes");
}
DisablePinchZoom will be fired before the onchange so zoom will be disable at the time the onchange is fired. On the onchange function, at the end you can restore the initial situation.
Tested on an iPhone 5S