When http://www.abc.com/~xyz gets called PerlAuthenHandler MyModule is invoked. MyModule code checks for IP after reading a file from xyz directory. If the host ip matches with the one in the file, it returns OK and the PerlAuthzHandler never gets called and the webpage is served to the user.
you may want to try using a PerlAccessHander for checking the IP, then combine that with Satisfy Any (as opposed to the Satisfy All default).
HTH
--Geoff
