Well, I followed the somewhat confusing instructions on this page: https://www.minibb.com/new_profile_field.html and I'm still having issues.

Basically, I did this:

1) Added a new field to the minibbtable_users called user_template
2) Modified setup_options.php with the following line:
'user_template'=>array(21,'user_template','template')
3) Added the following to bb_plugins.php:

$query = "SELECT * FROM Templates";
$result = mysql_query($query);
while($row = mysql_fetch_array($result))
{
$id = $row['pkTemplate'];
$templates[$id] = $row['sTemplate'];
}

$templateDropDown=makeValuedDropDown($templates,'template');

4) Modified user_dataform.html to have {$templateDropDown}

I'm getting the drop-down just fine -- I've viewed the source, and everything there is correct. What it's not doing is updating the value in the database. What did I forget to do?

The field should be named user_customtemplate i.e. it should contain the wording 'user_custom' at the beginning.

Everything else is your custom issue and we're supporting such issues only for the fee.