Is it possible to change between two fontawesome icons on hover?

In my templates I often use FontAwesome and I came up with this CSS trick

* > .fa-hover-show,
*:hover > .fa-hover-hidden {
  display: none;
}
*:hover > .fa-hover-show {
  display: inline-block;
}

Add both icons to the HTML; the default icon should have the fa-hover-hidden class while the hover icon one should have fa-hover-show.

<a href="#">
  <i class="fa fa-lock fa-hover-hidden"></i>
  <i class="fa fa-lock-open fa-hover-show"></i>
  <span class="fa-hover-hidden">Locked</span>
  <span class="fa-hover-show">Unlocked</span>
</a>

Given that the icon has a hover effect, it is likely that it is inside a button or link, in which case, a proper solution would be to also react to the change on :focus as well.

* > .fa-hover-show,
*:hover > .fa-hover-hidden,
*:focus > .fa-hover-hidden {
  display: none;
}
*:focus > .fa-hover-show,
*:hover > .fa-hover-show {
  display: inline-block;
}

You could toggle which one's shown on hover:

_HTML:

<a href="#" class="lock">
    <i class="icon-unlock"></i>
    <i class="icon-lock"></i>
</a>

_CSS:

.lock:hover .icon-unlock,
.lock .icon-lock {
    display: none;
}
.lock:hover .icon-lock {
    display: inline;
}

Or, you could change the content of the icon-unlock class:

.lock:hover .icon-unlock:before {
    content: "\f023";
}