@rodrigovip: For this you will need to create a child theme. You can use Generate Child Theme Plugin to create a child theme. After creating a child theme Go to => Child Theme Folder => style.css and add the following Code.
@font-face {
font-family: "FontAwesome";
font-weight: normal;
font-style : normal;
src : url("https://maxcdn.bootstrapcdn.com/font-awesome/4.3.0/fonts/fontawesome-webfont.eot?v=4.3.0");
src : url("https://maxcdn.bootstrapcdn.com/font-awesome/4.3.0/fonts/fontawesome-webfont.eot?#iefix&v=4.3.0") format("embedded-opentype"),
url("https://maxcdn.bootstrapcdn.com/font-awesome/4.3.0/fonts/fontawesome-webfont.woff2?v=4.3.0") format("woff2"),
url("https://maxcdn.bootstrapcdn.com/font-awesome/4.3.0/fonts/fontawesome-webfont.woff?v=4.3.0") format("woff"),
url("https://maxcdn.bootstrapcdn.com/font-awesome/4.3.0/fonts/fontawesome-webfont.ttf?v=4.3.0") format("truetype"),
url("https://maxcdn.bootstrapcdn.com/font-awesome/4.3.0/fonts/fontawesome-webfont.svg?v=4.3.0#fontawesomeregular") format("svg");
}
#menu-item-798 a {
visibility:hidden;
text-decoration:none;
}
#menu-item-798 a::before {
visibility:visible;
content:'\f0ad';
font-family:FontAwesome;
}
Let me know if this works out!
Kind Regards,
Skandha