I mean first i decompress the rpm. make changes.. then what???
Depends on which file(s) you changed. Please tell.
If it's inside the telnet.tar.bz2 :
"tar" it again to get telnet.tar.bz2
.. And do rpmbuild -bb telnet.spec
( Or rpmbuild -bs telnet.spec, if you want a new src.rpm.)
More info, please. Nobody can answer, when you are not telling,
what you did edit, and not telling, what you want to achieve.
Want an rpm package ? Or ?