Hi Andy -
re whether core file.. hmmm.. VM are quite "brutal" sometimes with their updates.. if you choose to adapt I would just check each update if the stockable variant plugin has been changed...
As to changing it - I don't know what your technical ability is but i will try and point you in the right direction...
This add to cart button is changed by the plugin for "availability" by Jquery
if ("disableadd" == stockhandle && stockable_'.$js_suffix.'[found_id].in_stock <= 0) {
$(".addtocart-bar>span").remove();
$(".addtocart-bar>div").remove();
$(".addtocart-bar>a.notify").remove();
$(".addtocart-bar").append(\'<a href="ind\'+\'ex.php?option=com_virtuemart&view=productdetails&layout=notify&virtuemart_product_id=\' + found_id + \'" class="notify">' . JText::_('COM_VIRTUEMART_CART_NOTIFY') . '</a>\');
} else {
var quantity = $(".addtocart-bar .quantity-input").val();
$(".addtocart-bar>span").remove();
$(".addtocart-bar>div").remove();
$(".addtocart-bar>a.notify").remove();
$(".addtocart-bar").append(\'<span class="quantity-box"><input type="text" class="quantity-input js-recalculate" name="quantity[]" value="1" /></span><span class="quantity-controls js-recalculate"><input type="button" class="quantity-controls quantity-plus" /><input type="button" class="quantity-controls quantity-minus" /></span><span class="addtocart-button"><input type="submit" name="addtocart" class="addtocart-button" value="'.JText::_('COM_VIRTUEMART_CART_ADD_TO').'" title="'.JText::_('COM_VIRTUEMART_CART_ADD_TO').'" /></span><div class="clear"></div>\');
Virtuemart.product($("form.product"));
}
$(".availability").remove();
if you look at the source of the css3 button we use you can see the html of the button is different
<div class="addtocart-bar FlexibleProductDetailsAddToCartBar">
<!-- <label for="quantity5" class="quantity_box">Quantity: </label> -->
<input type="hidden" value="1" name="quantity[]" class="quantity-input js-recalculate">
<span class="FlexibleCSS3Button">
<input type="submit" name="addtocart" value="Add to Cart" title="Add to Cart" class="addtocart-button FlexibleCSS3Button-text">
<span class="FlexibleCSS3Button-slide-text">
<span class="FlexibleProductDetailsInStock">product in stock</span>
<span class="FlexibleProductDetailsStockNumber">(150)</span>
</span>
<span class="FlexibleCSS3Button-icon-right"> <span></span></span>
</span>
<span class="FlexibleProductDetailsStockInfo">
</span>
<div class="clear"></div>
</div>
i.e. a couple of extra spans and a class added to allow the injection of the product in stock etc..
You would need to make the the html of the JS above match this..
if you look in
templates/YOUR_TEMPLATE/html/com_virtuemart/productdetails/default_addtocart.php from line 62 you'll see what I'm going on about..
Hope this gives you a few pointers..
Cheers