Change control panel entry domain to sub

[Smallserver]

Hi There,

Sorry if this is a dup, could not find it after half an hour of searching.

I installed ispcp and do my administration (login to ispcp) on http://www.mydomain.tld/
First of all, I want to change this to admin.mydomain.tld/ (I did not do this during installation. But how do I do that without installing from scratch?

Secondly, if I get it moved, can I use http://www.mydomain.tld as a normal domain, i.e. add it to ispcp as a user and put a website there?

Thanks in advance,
Herman