Because Joomla! is limited to some user fields that come default with install, we added an option in ARRA User Migrate to add more custom user fields in Joomla! 3.x. All these fields will be also visible under Joomla! User plugin named “User – Profile“. You should have this plugin activated in order to add/display and manage custom fields you will add.
By default, Joomla! will “see” only his fields and not ours, for this you need to hack a Joomla file – profile.php which is on this path: \plugins\user\profile\profile.php – , is the file were all custom user fields are recorded. Please also read this article: http://www.joomlarra.com/import-custom-user-fields-in-joomla-3-x/
We added a small change inside, Joomla! “will see” now if ARRA User Migrate component created fields are set as “Required” or “Disabled“. No need to alter this file if you just need the custom user field to be “Optional”.
When you do Joomla! upgrade, if profile.php file will be rewritten by Joomla, you should replace it again!