<div mnt-watch-product="ZAL-BE-DP521I09O-K11" mnt-watch-product-hide-class="disable-product">
 <button type="button" onclick="Monotote.show('ZAL-BE-DP521I09O-K11')">View details</button>
 <span>The product is not available</span>
</div>
<style>
 div span {
   display: none;
 }
 div.disable-product button {
   display: none;
 }
 div.disable-product span {
   display: initial;
 }
</style>