If you need to permanently change Apache DocumentRoot for just a single domain, you should do this as Admin.

Go to

http://[domain]:2222/CMD_CUSTOM_HTTPD?domain=[domain]

In the first window, under

Only add the few lines of the VirtualHost you need to insert.
Do not add a whole ..

Add the following line:

|?DOCROOT=/custom/document/root|

Don’t forget to put pipes at the start and at the end of this line. You’re done, default DocumentRoot value will be replaced with the path you specified!