[Phalynx]

Really nice Hack. It works, but I had to change 2 things:

Forum is named forum.php not index.php:

<if condition="$_REQUEST['e'] == 1 AND $bbuserinfo[userid]">
&nbsp; &nbsp;
<a href="forum.php?$session[sessionurl]e=0">$vbphrase[showhideforums_turnoff]</a></if>
<if condition="$_REQUEST['e'] != 1 AND $bbuserinfo[userid]">
&nbsp; &nbsp;
<a href="forum.php?$session[sessionurl]e=1">$vbphrase[showhideforums_turnon]</a>
</if>

After updating, go back to forumhome, instead of editmode again:
In forum.php (index.php) I added

header("Location: forum.php");

after

$DB_site->query("UPDATE user SET excludeforumids = '" . $bbuserinfo['excludeforumids'] . "' WHERE userid = '" . $bbuserinfo['userid'] . "' LIMIT 1");