change gui adress

[FidiBus]

from org. server-setup i have the host name:12-34-56-78.xyz.tld
after ispcp(1.0.2) i have: admin.12-34-56-78.xyz.tld
i know i can reach it with just the ip but all links for clients will have: 12-34-56-78.xyz.tld/???

i changed hostname to: 12.34.56.78 (rebbooted)
fixed manually all apache settings (all is working fine)
but postfix has: admin.12-34-56-78.xyz.tld
left and don´t accept just a ip if i reconfigure it.

but may it is more easy to do a new install with just the ip as hostname?
can i just run the setup again...or better clean before?
is it overall possible to install ispcp with just a ip as hostname?

thank you