Hi stefano,

It is not possible to achieve that through settings. However, you can template override the following theme file so that only site admins can view the custom field form.

JoomlaFolder/components/com_easydiscuss/themes/wireframe/composer/tabs/fields/heading.php
http://take.ms/BPjQV, http://take.ms/koZCw

Sorry but I explained myself badly.
I would like users to be able to write those information but once the post has been published, only the super user user sees them

Hey stefano,

In that case, you can ignore my previous reply.

In order to show the custom fields section in discussion page to super users only, you have to template override the following file
JoomlaFolder/components/com_easydiscuss/themes/wireframe/post/default.fields.php
http://take.ms/QgqoT