RESOLUTION
Parallels Plesk Sitebuilder for Linux/Unix:It is not possible in Sitebuilder interface but could be done directly on the server in Sitebuilder database. Before making any modification to database please do not forget to make a dump for it.
Template categories list is stored in 'template_category' table of Sitebuilder database (by default 'sitebuilder3'):
mysql> describe template_category;
+-------+--------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+-------+--------------+------+-----+---------+----------------+
| id | int(11) | | PRI | NULL | auto_increment |
| name | varchar(255) | | | | |
+-------+--------------+------+-----+---------+----------------+
2 rows in set (0.00 sec) So if you wish, for example, rename one of the categories you need just update appropriate record:
mysql> update template_category set name="NEW_NAME_FOR_CATEGORY" where id=<ID>;
Parallels Plesk Sitebuilder for Windows:
In Windows version category name should be changed directly for template itself in info.xml file. For example,
C:\Program Files\Parallels\Plesk\Sitebuilder\Repository\Design\TEMPLATE_NAME\info.xml:
.....
category="CATEGORY_NAME">
....
After that Sitebuilder application pool 'SitebuilderWebAppPool' should be restarted/recycled to apply the changes:
IIS -> Application pools -> SitebuilderWebAppPool -> right click 'Recycle'.