[Dr.CustUmz]

You want to search for

<img src="$stylevar[imgdir_statusicon]/$forum[imageprefix]forum_$forum[statusicon].gif" alt="" border="0" id="forum_statusicon_$forum[forumid]" />

replace with

<i class="fa fa_ICON"</i>

to set a diffent icon based on status use

$forum[statusicon]

which will return NEW / OLD
so you can do just an example

<if condition="$forum[statusicon] == 'new'">NEW ICON <else /> OLD ICON </if>

NOTE This will not allow you to double click the icon to mark the forum read, but if you look at the code you are replacing im sure you can figure it out

You know I've actually never thought to do this, and super easy for that matter. May add this to my fontawesomer addon =)