hi ,
i have made a mistake 
on the production enviourment by change tha host name .
after that i returned back the old name.
but i think this will not afeect the system until reboot the machine.
laso i tried to telnet the syetem by the host name not by the IP address and it works fine.
does this affect the system????????????????????????????????
Probably not. It will depend to some extent on how you resolve hostnames. If you resolve locally, or the DNS server has not been updated, then telnet will still work, even if the host name has changed.
I don't think you will have a problem though, unless the system does not complete a normal reboot. Even then (if you have a hang or crash) you will probably get away with it.
I presume you didn't down or detach any ethernet interfaces, so the change never went into effect and the next time the system boots it will re-read the original hostname, so all should be OK.
I think dukessd is correct, you will most likely come away with this without a big problem.... Lucky you 
And now NEVER NEVER do that again he 