I recently setup another webapp which uses /admin for configuration, unfortunately it's /admin conflicts with kolab's webadmin /admin
My solution was to change the following values
/usr/share/php/kolab/admin/include/headers.php
$topdir = '/kadmin'
/etc/apache2/vhosts.d/kolab-domain-base.include
Alias /kadmin "/var/www/kolab/htdocs/admin/"
<Location /kadmin>
now
https://www.domain.com/kadmin is for kolab's webadmin
make sure to modify the applicable template files in /etc/kolab/templates or your changes will be overwritten.