1. You don't need to modify a template at all.
2. Just go into Registration settings / Registration screen and set the Custom field prompt ( example picture below )

[Linked Image from sirdude.com]

I set it to hide and that really just HIDES it only @ registration, but because I fill it in, then it will always now show when they edit their PROFILE.

Then the only modification to do is in scripts/postlist.inc.php

On line 43 ( approx ), add the extra field to the list of fields to retrieve for each user:

"user_fields" => "t2.USER_TOPIC_VIEW_TYPE, t2.USER_TOPICS_PER_PAGE, t2.USER_POSTS_PER_TOPIC,USER_EXTRA_FIELD_1",

Then around line 837 you will see:
PHP Code

// Gotta clean out the [ and ], as they are keys to the .js parser. Also need to fix graemlin links
$postrow[$z]['tooltip'] = "";
if ($config['TOOLTIP_LENGTH'] && $config['TOOLTIP_LENGTH'] > 0) {

change that to this:
PHP Code

// Gotta clean out the [ and ], as they are keys to the .js parser. Also need to fix graemlin links
$postrow[$z]['tooltip'] = "";
if ($config['TOOLTIP_LENGTH'] && $config['TOOLTIP_LENGTH'] > 0 && $user['USER_EXTRA_FIELD_1'] == '1') {

this will allow the user to edit their profile and put 1 to enable the tooltip or 0 to not have it.

Then you make the board to always show it by default, but allow users to turn it off in their profile

2c