Hi,
yes but this is not simple, custom fields are composed from these files:
- administrator/com_jsn/helpers/fieldtype.php (here you can set Joomla XML to load field, output of search form, and search query)
- administrator/com_jsn/helpers/fieldtype.xml (here you can set parameters of field, this use Joomla XML sintax)
- administrator/com_jsn/models/fieldtype.php (optionally, if type not is Joomla native format you need to specify here, this file contain model of field inherit from JFormField Joomla class)

This is complex so I suggest you to simply modify the current select field type (administrator/com_jsn/helpers/selectlist.php)

Hi again.
I don´t know how to edit/set up xml or php.
Could you please help me make the select-fields (which are set to multiple options in profile) to be single (not multiple) in search-module?

Could you please help me make the select-fields (which are set to multiple options in profile) to be single (not multiple) in search-module?

Try to edit file /administrator/com_jsn/models/selectlist.php, at lines 142, 186 replace this:

$field->params->get('select_multiple',0)

with this

false

It is working perfectly!!! Thanks a lot

before line 215 add this code:

$option=array($option);

Excellent,
Thank you very much. Easyprofile is a great extension, and your support is the best