To create custom Plesk title bar text:
insert into misc(param, val) values('custom_title', 'My Custom Title')
Where 'My Custom Title' is the Plesk custom title bar text you wish to set.
To change custom Plesk title bar text:
update misc set val = 'New My Custom Title' where param='custom_title'
Where 'My Custom Title' is the Plesk custom title bar text you wish to set.
To delete custom Plesk title bar text:
delete from misc where param='custom_title'