You should simply be able to do the following:
<<linkreplace "text">>[img["animated-gif-url.gif?" + Date.now()]]<</linkreplace>>
Though, to make that simpler to use, you could make a widget out of it. For example:
<<widget "agif">>[img[$args[0] + "?" + Date.now()]]<</widget>>
Usage:
<<linkreplace "text">><<agif "animated-gif-url.gif">><</linkreplace>>
PS: Your postdisplay task is more complicated, and less thorough, than it needs to be. It would be better as:
postdisplay['gif-reloader'] = function () {
$('.gif-reload img').attr('src', function (i, src) {
return src.replace(/\?.*$/, '') + '?' + i + Date.now();
});
};