Some networks support virtual hosting, where you (or an IRCop) can set a virtual host for you. With a virtual host, people doing a /whois on you will see the virtual host information (exceptions are the IRCops who will see both the virtual and the real host information). As to other stuff, it depends on exactly what you're wanting to change/hide. Some information can be changed easily, while other information is almost (if not impossible) to hide (depending on who you're wanting to hide it from).